REST API

Development

with Node.js

Manage and Understand the Full Capabilities

of Successful REST Development

—

Second Edition

—

Fernando Doglio

REST API Development

with Node.js

Manage and Understand the Full

Capabilities of Successful REST

Development

Second Edition

FernandoDoglio

REST API Development with Node.js

ISBN-13 (pbk): 978-1-4842-3714-4 ISBN-13 (electronic): 978-1-4842-3715-1

https://doi.org/10.1007/978-1-4842-3715-1

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Printed on acid-free paper

FernandoDoglio

La Paz, Canelones, Uruguay

To my loving wife, without whom this book would’ve

never happened and to my beautiful boys, without whom

this book would’ve happened a lot sooner…

ank you!

v

About the Author �� xi

About the Technical Reviewer �� xiii

Acknowledgments ��xv

Introduction ��xvii

Table of Contents

Chapter 1: REST 101 �� 1

Where Did It All Start? �� 2

REST Constraints �� 4

Client–Server �� 4

Stateless �� 5

Cacheable �� 6

Uniform Interface �� 7

Layered System �� 9

Code-on-Demand �� 10

Resources, Resources, Resources �� 11

Representations �� 11

Resource Identier �� 14

Actions �� 15

Hypermedia intheResponse andMain Entry Point �� 20

Status Codes �� 26

REST vs� thePast �� 28

Summary�� 37

vi

Chapter 2: API Design Best Practices �� 39

What Denes aGood API? �� 39

Developer-Friendly �� 40

Communication’s Protocol �� 40

Easy-to-Remember Access Points �� 41

Uniform Interface �� 42

Extensibility �� 46

How Is Extensibility Managed? �� 46

Up-to-Date Documentation �� 50

Proper Error Handling �� 53

Phase 1: Development oftheClient �� 53

Phase 2: TheClient Is Implemented andBeing Used byEnd Users �� 55

Multiple SDK/Libraries �� 56

Security �� 57

Accessing theSystem �� 58

Scalability �� 66

Summary�� 70

Chapter 3: Node�js andREST �� 71

Asynchronous Programming �� 72

Async Advanced �� 76

Asynchronous I/O �� 81

Async I/O vs� Sync I/O �� 85

Simplicity �� 87

Dynamic Typing �� 88

Object-Oriented Programming Simplied�� 89

The new Class construct fromES6�� 91

Functional Programming Support �� 93

Duck Typing �� 94

Native Support forJSON �� 95

Table of ConTenTs

vii

npm: TheNode Package Manager �� 96

Who’s Using Node�js? �� 98

Summary�� 99

Chapter 4: Architecting aREST API �� 101

The Request Handler, thePre-Process Chain, andtheRoutes Handler �� 102

MVC: a�k�a� Model–View–Controller �� 107

Alternatives toMVC �� 112

Response Handler �� 116

Summary�� 119

Chapter 5: Working withModules �� 121

Our Alternatives �� 122

Request/Response Handling �� 122

Routes Handling �� 122

Middleware �� 123

Up-to-Date Documentation �� 125

Hypermedia ontheResponse �� 125

Response andRequest Validation �� 125

The List ofModules �� 125

Summary�� 172

Chapter 6: Planning Your REST API �� 173

The Problem �� 173

The Specications �� 177

Choosing theRight Modules fortheJob �� 188

Summary�� 189

Chapter 7: Developing Your REST API �� 191

Minor Changes tothePlan �� 192

Simplication oftheStore–Employee Relationship�� 192

Adding Swagger UI �� 192

Simplied Security �� 193

Table of ConTenTs

viii

A Small Backdoor forSwagger �� 193

MVC �� 194

Folder Structure �� 194

The Source Code �� 196

cong �� 197

Controllers �� 197

lib �� 228

Models �� 237

request_schemas �� 243

schemas �� 245

swagger-ui�� 254

Root Folder �� 255

Summary�� 259

Chapter 8: Testing your API �� 261

Testing 101�� 261

The Denition �� 261

The Tools �� 264

Best Practices �� 271

Testing withNode�js �� 272

Testing Without Modules �� 272

Mocha �� 275

Summary�� 282

Chapter 9: Deploying into Production �� 283

Different Environments �� 283

The Classical Development Workow�� 283

Tips forYour Production Environment �� 286

Table of ConTenTs

ix

Doing theActual Deployment �� 291

Shipit �� 292

What about Continuous Integration? �� 295

PM2 �� 296

Summary�� 302

Chapter 10: Troubleshooting �� 303

Asynchronous Programming �� 303

The Controllers Action’s Code �� 304

The Middleware Functions �� 306

Issues Conguring theSwagger UI �� 308

CORS: a�k�a� Cross-Origin Resource Sharing �� 310

Summary�� 314

Index �� 315

Table of ConTenTs

xi

About the Author

FernandoDogliohas worked as a developer for the past

13 years. In that time, he has come to love the Web and has

had the opportunity to work with most leading technologies,

such as PHP, Ruby on Rails, MySQL, Node.js, Angular.js,

AJAX, REST APIs, and others. For the past 4 years Fernando

has also been working as a Technical Manager and Technical

Lead for BigData projects.

In his spare time, Fernando likes to tinker, learn new

things, and write technical articles and books such as this

one. He’s also a big open source supporter, always trying to bring new people into that

realm. When not programming, he is spending time with his family.

Fernando can be contacted on Twitter @deleteman123 or online at

www.fernandodoglio.com.

xiii

About the Technical Reviewer

TakashiMukodais an international student at Purchase

College/State University of NewYork. Now, he is taking a

semester off and is back home in Japan. At Purchase College,

he majors in Mathematics/Computer Science and New

Media and has worked as a teaching assistant for computing

and mathematics courses.

Takashi likes playing the keyboard and going on hikes

in mountains to take pictures. His interest in programming

and art incites him to create multi-media art pieces. Some

of them are built with Processing and interact with human

motion and sounds.

(Website: http://www.takashimukoda.com)

xv

Acknowledgments

I’d like to thank the amazing technical reviewer involved in the project, Takashi Mukoda,

whose great feedback was a crucial contribution to the making of this book.

I’d also like to thank the rest of the Apress editorial team, whose guidance helped me

through the process of writing this, my first book.

xvii

Introduction

These days, everyone is finding a new way to interconnect systems; the Internet of

Things (IoT), for instance, is the new kid on the block, but who knows what will come

later.

The point is that in order to interconnect systems, as an architect, you’re better off

using standard methods that allow for a faster adoption of your technology. In particular,

APIs allow for the creation of standards and can work under known and well-tested core

technologies like HTTP.

If you add to that a well-defined style guide like REST, you’ve got yourself the means

to create a scalable, technology-agnostic, and uniform interface for your services to be

consumed by your clients.

Welcome to REST API Development with Node.js. This book will cover REST, API

development, and, finally, how these two mix up with Node.js.

Starting from a theoretical point of view, you’ll learn how REST came to be, who

created it, and its characteristics. Later, you’ll move toward the practical side by going

over API development and the lessons that years of experience from the community

have taught us. Finally, you’ll move into a fully practical approach, and you’ll see how

Node.js and its modules can help create a RESTful API.You’ll also get a taste of what

a real-world development flow would be like and what it would take to both test and

deploy your code into a production environment.

The final chapters will be 100% practical, going over a real-world example of a

RESTful API developed in Node.js. I will cover everything from the requirement-

gathering process, to tools selection, through actual development, and, finally, you’ll

land in troubleshooting-land, where I’ll discuss the different things that can go wrong

and how to tackle them.

Now sit back, relax, and enjoy the reading.

1

F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1_1

CHAPTER 1

REST 101

Nowadays, the acronym REST has become a buzzword, and as such, it’s being thrown

into the digital wind very carelessly by a lot of tech people without fully understanding

what it really means. Just because you can interact with a system using HTTP, and send

JSON back and forth, doesn’t mean it’s a RESTful system. REST is a lot more than that—

and that is what we’ll cover in this chapter.

Let’s start where it all began, with Roy Fielding’s paper, going over the main

characteristics of his idea. I’ll try to explain the main aspects of it, the constraints he

added, and why he added them. I’ll go over some examples and then jump backward

into the past, because even though REST has proven to be a huge jump forward

regarding distributed systems interconnection, before Fielding’s paper became popular,

developers were still looking for solutions to the problem: how to easily interconnect a

nonhomogeneous set of systems.

I’ll do a quick review of the options developers had back then to interconnect

systems, mainly going over SOAP and XML-RPC (the two main players before REST).

In the end, I’ll jump back to our current time, comparing the advantages that REST

brought us and thus showing why is it so popular today.

But first, a small clarification is in order: As you’ll read in just a few minutes, REST is

protocol-independent (as long as the protocol has support for a URI scheme), but for the

sake of this book and since we’re focusing on API design, let’s assume that the protocol

we’re using is HTTP, which will simplify explanations and examples. And as long as you

keep in mind that the same is true for other protocols (like FTP), then you’ll be fine.

2

Where Did It All Start?

This whole thing started with Roy Fielding, an American computer scientist born in

1965. He is one of the main authors of the HTTP protocol

1

(the protocol upon which the

entire Web infrastructure is based). He is also one of the co-authors of the Apache Web

server

2

and he was the chair of the Apache Software Foundation

3

for the first 3 years of its

existence.

So, as you can see, Fielding has made a lot of great contributions to the IT world,

especially regarding the Internet, but I think that his doctoral thesis is the thing that

received the most attention and made his name known among a lot of people who

otherwise wouldn’t have heard of him.

In the year 2000, Fielding presented his doctoral dissertation, Architectural Styles and

the Design of Network-based Software Architecture

4

. In it he coined the term REST, an

architectural style for distributed hypermedia systems.

Put simply, REST (short for REpresentational State Transfer) is an architectural

style defined to help create and organize distributed systems. The key word from that

definition should be style, because an important aspect of REST (which is one of the

main reasons books like this one exist) is that it is an architectural style—not a guideline,

not a standard, nor anything that would imply that there are a set of hard rules to follow

to end up having a RESTful architecture.

And because it is a style, and there is no Request for Comments (RFC) out there to

define it, it’s subject to misinterpretations from the people reading about it. Not only

that, but some go as far as to leave parts out and implement a subset of its features,

which in turn leads to a widespread and incomplete REST ideal, leaving out features that

would otherwise be useful and help your system’s users.

The main idea behind REST is that a distributed system, organized RESTfully, will

improve in the following areas:

• Performance: The communication style proposed by REST is meant

to be efficient and simple, allowing a performance boost on systems

that adopt it.

1

See https://www.ietf.org/rfc/rfc2616.txt.

2

See http://httpd.apache.org/.

3

See http://www.apache.org/.

4

See http://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm.

CHAPTER 1 REST 101

3

• Scalability of component interaction: Any distributed system should

be able to handle this aspect well enough, and the simple interaction

proposed by REST greatly allows for this.

• Simplicity of interface: A simple interface allows for simpler

interactions between systems, which in turn can grant benets like

the ones previously mentioned.

• Modiability of components: e distributed nature of the system,

and the separation of concerns proposed by REST (more on this in

a bit), allows for components to be modied independently of each

other at a minimum cost and risk.

• Portability: REST is technology- and language-agnostic, meaning

that it can be implemented and consumed by any type of technology

(there are some constraints that I’ll go over in a bit, but no specic

technology is enforced).

• Reliability: e stateless constraint proposed by REST (more on this

later) allows for the easier recovery of a system after failure.

• Visibility: Again, the stateless constraint proposed has the added

benefit of improving visibility, because any monitoring system

doesn’t need to look further than a single request message to

determine the full state of said request (this will become clear once I

talk about the constraints in a bit).

From this list, some direct benefits can be extrapolated.

• A component-centric design allows you to make systems that are

very fault tolerant. Having the failure of one component not affect the

entire stability of the system is a great benefit for any system.

• Interconnecting components is quite easy, minimizing the risks

when adding new features or scaling up or down.

• A system designed with REST in mind will be accessible to a wider

audience, thanks to its portability (as described earlier).With a generic

interface, the system can be used by a wider range of developers.

To achieve these properties and benefits, a set of constraints were added to REST to

help define a uniform connector interface.

CHAPTER 1 REST 101

4

REST Constraints

According to Fielding, there are two ways to define a system. One approach is to start from a

blank slate, an empty whiteboard, with no initial knowledge of the system being built or the

use of familiar components until the needs are satisfied. A second approach is to start with

the full set of needs for the system, and constraints are added to individual components

until the forces that influence the system are able to interact in harmony with each other.

REST follows the second approach. To define a REST architecture, a null-state is

initially defined—a system that has no constraints whatsoever and where component

differentiation is nothing but a myth—and constraints are added one by one.

Client–Server

The first constraint to be added is one of the most common ones on network-based

architectures: client–server. A server is in charge of handling a set of services, and

it listens for requests regarding said services. The requests, in turn, are made via a

connector by a client system needing one of those services (see Figure1-1).

The main principle behind this constraint is the separation of concerns. It allows for

the separation of front-end code (representation and possible UI-related processing of

the information) from the server-side code, which should take care of storage and server-

side processing of the data.

This constraint allows for the independent evolution of both components, offering a

great deal of flexibility by letting client applications improve without affecting the server

code and vice-versa.

Figure 1-1. Client–Server architecture diagram

CHAPTER 1 REST 101

5

Stateless

The constraint to be added on top of the previous one is the stateless constraint (see

Figure1-2). Communication between client and server must be stateless, meaning that

each request done from the client must have all the information required for the server

to understand it, without taking advantage of any stored data.

This constraint represents several improvements for the underlying architecture:

• Visibility: Monitoring the system becomes easy when all the

information required is inside the request.

• Scalability: By not having to store data between requests, the server

can free resources faster.

• Reliability: As mentioned earlier, a system that is stateless can recover

from a failure much easier than one that isn’t, since the only thing to

recover is the application itself.

• Easier implementation: Writing code that doesn’t have to manage

stored-state data across multiple servers is much easier to do, thus

the full server-side system becomes simpler.

Although at first glance this constraint might seem nothing but good, as what

normally happens, there is a trade-off. On one hand, benefits are gained by the system,

but on the other side, network traffic could potentially be harmed by adding a minor

overhead on every request from sending repeated state information. Depending on the

type of system being implemented, and the amount of repeated information, this might

not be an acceptable trade-off.

CHAPTER 1 REST 101

6

Cacheable

The cacheable constraint is added to the current set of constraints (see Figure1-3). It

proposes that every response to a request must be explicitly or implicitly set as cacheable

(when applicable).

By caching the responses, there are some obvious benefits that get added to the

architecture: on the server side, some interactions (a database request, for example)

are completely bypassed while the content is cached. On the client side, an apparent

improvement of performance is perceived.

The trade-off with this constraint is the possibility of cached data being stale, due

to poor caching rules. This constraint is, again, dependent on the type of system being

implemented.

Figure 1-2. Representation of the stateless constraint

CHAPTER 1 REST 101

7

Note Figure1-3 shows the cache as an external layer between the clients and

the servers. This is only one possible implementation of it. The cache layer could

be living inside the client (i.e., browser cache) or inside the servers themselves.

Uniform Interface

One of REST’s main characteristics and winning points when compared to other

alternatives is the uniform interface constraint. By keeping a uniform interface between

components, you simplify the job of the client when it comes to interacting with

your system (see Figure1-4). Another major winning point here is that the client’s

implementation is independent of yours, so by defining a standard and uniform

interface for all of your services, you effectively simplified the implementation of

independent clients by giving them a clear set of rules to follow.

Said rules are not part of the REST style, but there are constraints that can be used to

create such rules for each individual case.

Figure 1-3. Representation of a client-stateless-cache-server architecture

CHAPTER 1 REST 101

8

This benefit doesn’t come without a price, though; as with many other constraints,

there is a trade-off here: having a standardized and uniform interface for all interactions

with your system might harm performance when a more optimized form of communication

exists. Particularly, the REST style is designed to be optimized for the Web, so the more

you move away from that, the more inefficient the interface can be.

Note To achieve the uniform interface, a new set of constraints must be added

to the interface: identification of resources, manipulation of resources through

representation, self-descriptive messages, and hypermedia as the engine of

application state (a.k.a. HATEOAS). I’ll discuss some of these constraints shortly.

Figure 1-4. Different client types can interact seamlessly with servers thanks to the

uniform interface

CHAPTER 1 REST 101

9

Layered System

REST was designed with the Internet in mind, which means that an architecture that

follows REST is expected to work properly with the massive amount of traffic that exists

in the web of webs.

To achieve this, the concept of layers is introduced (see Figure1-5). By separating

components into layers, and allowing each layer to only use the one below and to

communicate its output to the one above, you simplify the system’s overall complexity

and keep component coupling in check. This is a great benefit in all type of systems,

especially when the complexity of such a system is ever-growing (e.g., systems with

massive amounts of clients, systems that are currently evolving, etc.).

The main disadvantage of this constraint is that for small systems, it might add

unwanted latency into the overall data flow, due to the different interactions between

layers.

Figure 1-5. Example of a multilayered architecture

CHAPTER 1 REST 101

10

Code-on-Demand

Code-on-demand is the only optional constraint imposed by REST, which means that an

architect using REST can choose whether or not to use this constraint and either gains its

advantages or suffers its disadvantages.

With this constraint, the client can download and execute code provided by the

server (such as Java applets, JavaScript scripts, etc.). In the case of REST APIs (on which

this book focuses), this constraint seems unnecessary, because the normal thing for an

API client to do is just get information from an endpoint, and then process it however

needed; but for other uses of REST, like web servers, a client (i.e., a browser) will

probably benefit from this constraint (see Figure1-6).

All of these constraints provide a set of virtual walls within which an architecture can

move and still gain the benefits of the REST design style.

But let’s take a step back. I initially defined REST as a design style for

representational state transfer; in other words, you transfer the state of things by using

some kind of representation. But what are these “things”? The main focus of a REST

architecture is the resources, the owners of the state that you’re transferring. Just like in a

real state (almost), it’s all about resources, resources, resources.

Figure 1-6. How some clients might execute the code-on-demand, whereas others

might not

CHAPTER 1 REST 101

11

Resources, Resources, Resources

The main building blocks of a REST architecture are the resources. Anything that can be

named can be a resource (a web page, an image, a person, a weather service report, etc.).

Resources define what the services are going to be about, the type of information that is

going to be transferred, and their related actions. The resource is the main entity from

which everything else is born.

A resource is the abstraction of anything that can be conceptualized (from an image

file, to a plain text document). The structure of a resource is shown in Table1-1.

Representations

At its core, a representation is a set of bytes, and some metadata that describes these

bytes. A single resource can have more than one representation; just think of a weather

service report (which could act as a possible resource).

The weather report for a single day could potentially return the following

information:

• The date the report is referencing

• e maximum temperature for the day

• e minimum temperature for the day

• e temperature unit to be used

• A humidity percentage

• A code indicating how cloudy the day will be (e.g., high, medium, low)

Table 1-1. Resource Structure Description

Property Description

Representations It can be any way of representing data (binary, JSON, XML, etc.). A single resource

can have multiple representations.

Identier A URL that retrieves only one specic resource at any given time.

Metadata Content-type, last-modied time, and so forth.

Control data Is-modied-since, cache-control.

CHAPTER 1 REST 101

12

Now that the resource’s structure is defined, here are a few possible representations

of the same resource:

JSON

{

"date": "2014-10-25",

"max_temp": 25.5,

"min_temp": 10.0,

"temp_unit": "C",

"humidity_percentage": 75.0,

"cloud_coverage": "low"

}

XML

<?xml version='1.0' encoding="UTF-8" ?>

<root>

<temp_unit value="C" />

<humidity_percentage value="75.0" />

<cloud_coverage value="low" />

<min_temp value="10.0" />

<max_temp value="25.5" />

</root>

Custom pipe-separated values:

2014-10-25|25.5|10.0|C|75.0|low

And there could be many more. They all successfully represent the resource

correctly; it is up to the client to read and parse the information. Even when the

resource has more than one representation, it is common for clients (due to simplicity of

development) to only request one of them. Unless you’re doing some sort of consistency

check against the API, there is no point in requesting more than one representation of

the same resource, is there?

There are two very popular ways to let the client request a specific representation on

a resource that has more than one. The first one directly follows the principles described

by REST (when using HTTP as a basis), called content negotiation, which is part of the

HTTP standard. The second one is a simplified version of this, with limited benefits. For

the sake of completeness, I’ll quickly go over them both.

CHAPTER 1 REST 101

13

Content Negotiation

As mentioned, this methodology is part of the HTTP standard,

5

so it’s the preferred way

according to REST (at least when focused on API development on top of HTTP). It is also

more flexible and provides further advantages than the other method.

It consists of the client sending a specific header with the information of the different

content types (or types of representations) supported, with an optional indicator of how

supported/preferred that format is.

Let’s look at an example from the “Content Negotiation” page on Wikipedia

6

:

Accept: text/html; q=1.0, text/*; q=0.8, image/gif; q=0.6, image/jpeg;

q=0.6, image/*; q=0.5, */*; q=0.1

This example is from a browser configured to accept various types of resources, but

preferring HTML over plain text and GIF or JPEG images over other types, but ultimately

accepts any other content type as a last resort.

On the server side, the API is in charge of reading this header and finding the best

representation for each resource, based on the client’s preferences.

Using File Extensions

Even though this approach is not part of the REST proposed style, it is widely used and a

fairly simple alternative to the somewhat more complex other option, so I’ll cover it anyway.

During the last few years, using file extensions has become an alternative preferred

over using content negotiation; it is a simpler version and it doesn’t rely on a header

being sent; instead, it works with the concept of file extensions.

The extension portion of the file’s name indicates the content type to the operating

system and any other software trying to use it; so in the following case, the extension

added to the resource’s URL (unique identifier) indicates to the server the type of

representation wanted.

GET /api/v1/books.json

GET /api/v1/books.xml

Both identifiers reference the same resource—the list of books, but they request a

different representation of it.

5

See http://tools.ietf.org/html/rfc7231#section-5.3.

6

See https://en.wikipedia.org/wiki/Content_negotiation

CHAPTER 1 REST 101

14

Note This approach might seem easier to implement, and even understand, by

humans, but it lacks the flexibility added by content negotiation and should only be

used if there is no real need for complex cases where multiple content types might

be specified with their related preference.

Resource Identifier

The resource identifier should provide a unique way of identification at any given

moment and it should provide the full path to the resource. A classic mistake is to

assume it’s the resource’s ID on the storage medium used (i.e., the ID on the database).

This means that you cannot consider a simple numeric ID as a resource identifier; you

must provide the full path, and because we’re basing REST on HTTP, the way to access

the resource it to provide its full URI (unique resource identifier).

There is one more aspect to consider: the identifier of each resource must be able to

reference it unequivocally at any given moment in time. This is an important distinction,

because a URI like the following might reference Harry Potter and the Half Blood Prince

for a certain period of time, and then Harry Potter and the Deathly Hollows 1 year later.:

GET /api/v1/books/last

This renders that URI as an invalid resource ID.Instead, each book needs a unique

URI that is certain to not change over time; for example:

GET /api/v1/books/j-k-rowling/harry-potter-and-the-deathly-hollows

GET /api/v1/books/j-k-rowling/harry-potter-and-the-half-blood-prince

The identifiers are unique here, because you can safely assume that the author won’t

publish more books with the same title.

And to provide a valid example for getting the last book, you might consider doing

something like this:

GET /api/v1/books?limit=1&sort=created_at

The preceding URI references the lists of books, and it asks for only one, sorted by its

publication date, thus rendering the last book added.

CHAPTER 1 REST 101

15

Actions

Identifying a resource is easy: you know how to access it and you even know how to

request for a specific format (if there is more than one); but that’s not all that REST

proposes. Since REST is using the HTTP protocol as a standing point, the latter provides

a set of verbs that can be used to reference the type of action being done over a resource.

There are other actions, aside from accessing, that a client app can take in the

resources provided by an API; these depend on the service provided by the API.These

actions could potentially be anything, just like the type of resources handled by the

system. Still, there is a set of common actions that any system that is resource-oriented

should be able to provide: CRUD (create, retrieve, update, and delete) actions.

These so-called actions can be directly mapped to the HTTP verbs, but REST

does not enforce a standardized way to do so. However, there are some actions that

are naturally derived by the verb and others that have been standardized by the API

development community over the years, as shown in Table1-2.

That said, a client may or may not support all of these actions; it depends on what

needs to be achieved. For instance, web browsers—a clear and common example of a

REST client—only have support for GET and POST verbs from within the HTML code

of a page, such as links and forms (although using the XMLHttpRequest object from

JavaScript would provide support for the major verbs mentioned earlier).

Table 1-2. HTTP Verbs and Their Proposed Actions

HTTP Verb Proposed Action

GET Access a resource in a read-only mode

POST Normally used to send a new resource into the server (create action)

PUT Normally used to update a given resource (update action)

DELETE Used to delete a resource

HEAD Not part of the CRUD actions, but the verb is used to ask if a given resource

exists without returning any of its representations

OPTIONS Not part of the CRUD actions, but used to retrieve a list of available verbs on a

given resource (i.e., What can the client do with a specic resource?)

CHAPTER 1 REST 101

16

Note The list of verbs and their corresponding actions are suggestions. For

instance, there are some developers who prefer to switch PUT and POST, by having

PUT add new elements and POST update them.

Complex Actions

CRUD actions are normally required, but they’re just a very small subset of the entire

spectrum of actions that a client can do with a specific resource or set of resources.

For instance, take common actions like searching, filtering, working with

subresources (e.g., the books of an author, the reviews of a book, etc.), sharing a

blogpost, and so forth. All of these actions fail to directly match one of the verbs that I

mentioned.

The first solution that many developers succumb to is to specify the action taken as

part of the URL; so you might end up with things like the following:

GET /api/v1/blogpost/12342/like

GET /api/v1/books/search

GET /api/v1/authors/filtering

Those URLs break the URI principle, because they’re not referencing a unique

resource at any given time; instead, they’re referencing an action on a resource (or

group of resources). They might seem like a good idea at first, but in the long run, and

if the system keeps on growing, there will be too many URLs, which will increase the

complexity of the client using the API.

So to keep things simple, use the following rule of thumb: Hide the complexity of your

actions behind the “?”.

This rule can apply to all verbs, not just GET, and can help achieve complex actions

without compromising the URL complexity of the API.For the preceding examples, the

URIs could become something like this:

PUT /api/v1/blogposts/12342?action=like

GET /api/v1/books?q=[SEARCH-TERM]

GET /api/v1/authors?filters=[COMMA SEPARATED LIST OF FILTERS]

CHAPTER 1 REST 101

17

Notice how the first one changed from a GET to a PUT due to the fact that the action

is updating a resource by linking it.

But what happens when the “?” is not enough?

When the complexity of your actions is too much for the “?”, there are some

alternatives that walk the line when it comes to REST-compliant solutions. Some of them

might not be ideal or even desired for your API design, but when reality hits you need to

do the best you can and that also includes figuring out if your use case actually fits inside

REST or if you need to go another route.

Use Collection ofActions

An alternative way of dealing with complex actions inside your API is to treat them as

resource collections. Granted, this is a bit of a stretch to what an action actually is, but

like I said, we’re walking the line here guys.

What this provides, is a valid interface for you to send commands to your resources

following a REST-like approach.

For example, say you want to reboot a VM, you can do something like the following:

POST /virtual-machines/<your-vm-id>/reboots

{

"When": "now"

}

This would effectively send a reboot command to your VM, telling it to reboot right

now. Notice the use of the POST verb here; there are couple reasons why I used that one

and not others:

1. Since we’re treating actions as resources, executing a new action

is the equivalent of creating a new resource inside the action’s

collection

2. POST is not an idempotent operation, which fits this use case,

since we can’t be certain about the side effects your complex

actions could have.

You could even extend this concept a bit further and provide an actual functionality

to other verbs on this endpoint, such as GET, so something like this:

GET /virtual-machines/<your-vm-id>/reboots

CHAPTER 1 REST 101

18

would provide an output detailing the list of reboots created or, put another way, a

list of times the action was executed:

{

"reboots": [

{ "received": "2001-10-23 13:30:00+0100", "params": { "when": "now" } },

{ "received": "2001-12-03 03:30:00+0100", "params": { "when": "5 min" } },

{ "received": "2002-10-23 13:30:00+0100", "params": { "when": "now" } }

]

}

Furthermore, each action could provide an endpoint to return information about it,

such as documentation to help developers using them. For instance, a request such as:

GET /virtual-machines/<your-vm-id>/reboots/1

could return something like:

{

"last-executed": "2018-02-23 15:02:02+0300",

"params": {

"when": {

"Required": true,

"Docs": “Describes the system reboot needs to take place,

relative to the moment the action is processed”

}

Another classic problematic endpoint that REST APIs tend to have is the so-called

“search endpoint,” one that can’t always fit inside our resource-based schema.

And for this, we have a couple of options.

CHAPTER 1 REST 101

19

Single-Entity Searches

If the search functionality is only going to return, and overall deal with, one kind of

entity, or if you’re going to provide scoped searches (meaning you will always be

searching on specific collections), then you can probably hide the search feature behind

the listing endpoint and use GET requests with search parameters

GET /books/?q=Harry pott&p=1&size=10

The previous example simply hijacks the listing endpoint and adds the ability to

filter the results but accepting a search string. These parameters could even be optional,

rendering this endpoint quite powerful and versatile.

Note The endpoint you define for your search functionality does not ensure the

type of results you’ll get, that will depend on the underlying technology used. If

you’re looking for simple searches, a quick SQL query can give you the results

you’re looking for. But if you need something more complex, I would suggest

looking into solutions such as Elastic.

Multi-Entity Searches

Now, if instead of just looking for books, you actually want your user to look for books

and also for author’s bios, and client names. All at the same time and have those results

all mixed in as one single list. Then there is no real easy way to relate this type of search

to a single resource, is there?

In this case, the only option that we have is to bite the bullet and break the mantra;

in other words, create an endpoint that references the actual action instead of a single

resource, i.e:

GET /search?q=Harry&p=1&size=10

If you can, and as long as it makes sense, always try to use endpoints such as

GET/action to provide information about the action and POST /action to perform it.

In the end, if you end up having to “bite the bullet” a lot while designing the

endpoints of your system, then maybe REST is not the best paradigm for you.

CHAPTER 1 REST 101

20

Hypermedia intheResponse andMain Entry Point

To make REST’s interface uniform, several constraints must be applied. One of them is

Hypermedia as the Engine of Application State, also known as HATEOAS. I’ll go over what

that concept means, how it is meant to be applied by a RESTful system, and finally, how

you end up with a great new feature that allows any RESTful system client to start the

interaction knowing only a single endpoint of the entire system (the root endpoint).

Again, the structure of a resource contains a section called metadata; inside that

section, the representation of every resource should contain a set of hypermedia links

that let the client know what to do with each resource. By providing this information in

the response itself, the next steps any client can take are there, thus providing an even

greater level of decoupling between client and server.

Changes to the resource identifiers, or added and removed functionalities, can

be provided through this method without affecting the client at all, or at worst, with

minimal impact.

Think of a web browser: all it needs to help a user navigate through a favorite

site is the home page URL; after that, the following actions are presented inside the

representation (HTML code) as links. Those are the only logical next steps that the user

can take, and from there, new links will be presented, and so on.

In the case of a RESTful service, the same thing can be said: by calling upon the main

endpoint (also known as bookmark or root endpoint), the client will discover all possible

first steps (normally things like resource lists and other relevant endpoints).

Let’s look at an example in Listing 1-1.

Root endpoint: GET /api/v1/

Listing 1-1. Example of a JSON Response from the Root Endpoint

{

"metadata": {

"links": {

"books": {

"uri": "/books",

"content-type": "application/json"

},

"authors": {

"uri": "/authors",

CHAPTER 1 REST 101

21

"content-type": "application/json"

}

Now let’s look at the books list endpoint’s results in Listing 1-2: GET /api/v1/books

Listing 1-2. Example of Another JSON Response with Hyperlinks to Other

Resources

{

"resources": [

{

"title": "Harry Potter and the Half Blood prince",

"description": "......",

"author": {

"name": "J.K.Rowling",

"metadata": {

"links": {

"data": {

"uri": "/authors/j-k-rowling",

"content-type": "application/json"

},

"books": {

"uri": "/authors/j-k-rowling/books",

"content-type": "application/json"

}

},

"copies": 10

},

{

"title": "Dune",

"description": "......",

"author": {

CHAPTER 1 REST 101

22

"name": "Frank Herbert",

"metadata": {

"links": {

"data": {

"uri": "/authors/frank-herbert",

"content-type": "application/json"

},

"books": {

"uri": "/authors/frank-herbert/books",

"content-type": "application/json"

}

},

"copies": 5

}

],

"total": 100,

"metadata": {

"links": {

"next": {

"uri": "/books?page=1",

"content-type": "application/json"

}

There are three sections highlighted in preceding example (Listing 1-2); those are the

links returned on the response. With that information, the client application knows the

following logical steps:

1. How to get the information from the books authors

2. How to get the list of books by the authors

3. How to get the next page of results

CHAPTER 1 REST 101

23

Note that the full list of authors is not accessible through this endpoint; this is

because for this particular use case, it’s not needed, so the API just doesn’t return it. It

was present on the root endpoint, though, so if the client needs it when displaying the

information to the end-user, it should still have it available.

Each link from the preceding example contains an attribute specifying the content-

type of the representation of that resource. If the resources have more than one

possible representation, the different formats could be added as different links inside

each resource’s metadata element, letting the client choose the most adequate to the

current use case, or the type could change based on the client’s preferences (content

negotiation).

Note that the earlier JSON structure (more specifically, the metadata elements’

structure) is not important. The relevant part of the example is the information

presented in the response. Each server has the freedom to design the structure as

needed.

Not having a standard structure might harm the developer experience while

interacting with your system, so it might be a good idea to adopt one. This is certainly not

enforced by REST, but it would be a major point in favor of your system. A good standard

to adopt in this case would be Hypertext Application Language, or HAL,

7

which tries

to create a standard for both XML and JSON when representing resources with those

languages.

A Few Notes onHAL

HAL tries to define a representation as having two major elements: resources and links.

According to HAL, a resource has links, embedded resources (other resources

associated to their parent), and a state (the actual properties that describe the resource).

On the other hand, links have a target (the URI), a relation, and some other optional

properties to deal with deprecation, content negotiation, and so forth.

7

See http://stateless.co/hal_specification.html.

CHAPTER 1 REST 101

24

Listing 1-3 shows the preceding example represented using the HAL format.

Listing 1-3. JSON Response Following the HAL Standard

{

"_embedded": [

{

"title": "Harry Potter and the Half Blood prince",

"description": "......",

"copies": 10,

"_embedded": {

"author": {

"name": "J.K.Rowling",

"_links": {

"self": {

"href": "/authors/j-k-rowling",

"type": "application/json+hal"

},

"books": {

"href": "/authors/j-k-rowling/books",

"type": "application/json+hal"

}

},

{

"title": "Dune",

"description": "......",

"copies": 5,

"_embedded": {

"author": {

"name": "Frank Herbert",

CHAPTER 1 REST 101

25

"_links": {

"self": {

"href": "/authors/frank-herbert",

"type": "application/json+hal"

},

"books": {

"href": "/authors/frank-herbert/books",

"type": "application/json+hal"

}

],

"total": 100,

"_links": {

"self": {

"href": "/books",

"type": "application/json+hal"

},

"next": {

"href": "/books?page=1",

"type": "application/json+hal"

}

The main change in Listing 1-3 is that the actual books have been moved inside an

element called "_embedded", as the standard dictates, since they’re actual embedded

documents inside the represented resource, which is the list of books (the only property

that belongs to the resource is "total", representing the total number of results). The

same can be said for the authors, now inside the "_embedded" element of each book.

CHAPTER 1 REST 101

26

Status Codes

Another interesting standard that REST can benefit from when based on HTTP is the

usage of HTTP status codes.

8

A status code is a number that summarizes the response associated to it. There

are some common ones, like 404 for “Page not found,” or 200 for “OK,” or the

always helpful 500 for “Internal server error” (that was irony, in case it wasn’t clear

enough).

A status code is helpful for clients to begin interpreting the response, but in most

cases, it shouldn’t be a substitute for it. As the API owner, you can’t really transmit

in the response what exactly caused a crash on your side by just replying with the

number 500. There are some cases, though, when a number is enough, like 404;

although a good response will always return information that should help the client

solve the problem (with a 404, a link to the home page or the root URL are good places

to start).

These codes are grouped in five sets, based on their meaning:

• 1xx: Informational and only defined under HTTP 1.1.

• 2xx: e request went OK, here’s your content.

• 3xx: e resource was moved somehow to somewhere.

• 4xx: e source of the request did something wrong.

• 5xx: The server crashed due to some error in its code.

With that in mind, Table1-3 lists some classic status codes that an API could

potentially use.

8

See http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html.

CHAPTER 1 REST 101

27

Table 1-3. HTTP Status Codes and Their Related Interpretation

Status Code Meaning

200 OK. The request went ne and the content requested was returned. This is normally

used on GET requests.

201 Created. The resource was created and the server has acknowledged it. It could be

useful on responses to POST or PUT requests. Additionally, the new resource could be

returned as part of the response body.

204 No content. The action was successful but there is no content returned. Useful for

actions that do not require a response body, such as a DELETE action.

301 Moved permanently. This resource was moved to another location and the location is

returned. This header is especially useful when URLs change over time (maybe due

to a change in version, a migration, or some other disruptive change), keeping the old

ones and returning a redirection to the new location allows old clients to update their

references in their own time.

400 Bad request. The request issued has problems (for example, might be lacking some

required parameters). A good addition to a 400 response might be an error message

that a developer can use to x the request.

401 Unauthorized. Especially useful for authentication when the requested resource is not

accessible to the user owning the request.

403 Forbidden. The resource is not accessible, but unlike 401, authentication will not

affect the response.

404 Not found. The URL provided does not identify any resource. A good addition to this

response could be a set of valid URLs that the client can use to get back on track (root

URL, previous URL used, etc.).

405 Method not allowed. The HTTP verb used on a resource is not allowed—for instance,

doing a PUT on a resource that is read-only.

500 Internal server error. A generic error code when an unexpected condition is met and

the server crashes. Normally, this response is accompanied by an error message

explaining what went wrong.

CHAPTER 1 REST 101

28

Note To see the full list of HTTP status codes and their meanings, please refer to

the RFC of HTTP 1.1.

9

REST vs. thePast

Before REST was all cool and hip, and every business out there wanted to provide their

clients with a RESTful API in their service, there were other options for developers who

wanted to interconnect systems. These are still being used on old services or by services

that required their specific features, but less and less so every year.

Back in the 1990s, the software industry started to think about system

interoperability and how two (or more) computers could achieve it. Some solutions

were born, such as COM,

10

created by Microsoft, and CORBA,

11

created by the Object

Management Group. These were the first two implementations back then, but they had a

major issue: they were not compatible with each other.

Other solutions arose, like RMI (Remote Method Invocation), but it was meant

specifically for Java, which meant it was technology-dependent, and hadn’t really caught

up with the development community.

By 1997, Microsoft decided to research solutions that would use XML as the main

transport language and would allow systems to interconnect using RPC (Remote

Procedure Call) over HTTP, thus achieving a somewhat technology-independent

solution that would considerably simplify system interconnectivity. That research gave

birth to XML-RPC around 1998.

Listing 1-4 is a classic XML-RPC request taken from Wikipedia:

12

9

See http://tools.ietf.org/html/rfc7231#section-6.

10

See https://en.wikipedia.org/wiki/Component_Object_Model

11

See http://www.corba.org/.

12

See http://en.wikipedia.org/wiki/XML-RPC.

CHAPTER 1 REST 101

29

Listing 1-4. Example of an XML-RPC Request

<?xml version="1.0"?>

<methodName>examples.getStateName</methodName>

<param>

</param>

</params>

</methodCall>

Listing 1-5 shows a possible response.

Listing 1-5. Example of an XML-RPC Response

<?xml version="1.0"?>

<param>

<value><string>South Dakota</string></value>

</param>

</params>

</methodResponse>

From the examples shown in Listing 1-4 and Listing 1-5, it is quite clear that the

messages (both requests and responses) were overly verbose, something that was

directly related to the use of XML.There are implementations of XML-RPC that exist

today for several operating systems and programming languages, like Apache XML-

RPC

13

(written in Java), XMLRPC-EPI

14

(written in C), and XML-RPC-C

15

for C and C++

(see Figure1-7).

13

See http://ws.apache.org/xmlrpc/.

14

See http://xmlrpc-epi.sourceforge.net.

15

See http://xmlrpc-c.sourceforge.net/.

CHAPTER 1 REST 101

30

After XML-RPC became more popular, it mutated into SOAP,

16

a more standardized

and formalized version of the same principle. SOAP still uses XML as the transport

language, but the message format is now richer (and therefore complex). Listing 1-6 is an

example from W3C’s specification page on SOAP:

Listing 1-6. Example of a SOAP Request

<?xml version='1.0' ?>

<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope">

<env:Header>

<m:reservation xmlns:m="http://travelcompany.example.org/reservation"

env:role="http://www.w3.org/2003/05/soap-envelope/role/next"

env:mustUnderstand="true">

<m:reference>uuid:093a2da1-q345-739r-ba5d-pqff98fe8j7d</m:reference>

<m:dateAndTime>2001-11-29T13:20:00.000-05:00</m:dateAndTime>

</m:reservation>

Figure 1-7. Diagram showing the basic architecture of an XML-RPC

interaction

16

See http://www.w3.org/TR/soap/.

CHAPTER 1 REST 101

31

<n:passenger xmlns:n="http://mycompany.example.com/employees"

env:role="http://www.w3.org/2003/05/soap-envelope/role/next"

env:mustUnderstand="true">

<n:name>Åke Jógvan Øyvind</n:name>

</n:passenger>

</env:Header>

<env:Body>

<p:itinerary

xmlns:p="http://travelcompany.example.org/reservation/travel">

<p:departure>

<p:departing>New York</p:departing>

<p:arriving>Los Angeles</p:arriving>

<p:departureDate>2001-12-14</p:departureDate>

<p:departureTime>late afternoon</p:departureTime>

<p:seatPreference>aisle</p:seatPreference>

</p:departure>

<p:return>

<p:departing>Los Angeles</p:departing>

<p:arriving>New York</p:arriving>

<p:departureDate>2001-12-20</p:departureDate>

<p:departureTime>mid-morning</p:departureTime>

<p:seatPreference/>

</p:return>

</p:itinerary>

<q:lodging

xmlns:q="http://travelcompany.example.org/reservation/hotels">

<q:preference>none</q:preference>

</q:lodging>

</env:Body>

</env:Envelope>

CHAPTER 1 REST 101

32

Figure1-8 shows the basic structure of the example from Listing 1-6.

SOAP services are actually dependent on another technology called Web Service

Description Language (WSDL). An XML-based language, it describes the services

provided to clients that want to consume them.

Listing 1-7 is an annotated WSDL example taken from the W3C web site.

17

Listing 1-7. WSDL Example

<?xml version="1.0"?>

<wsdl:definitions name="EndorsementSearch"

targetNamespace="http://namespaces.snowboard-info.com"

xmlns:es="http://www.snowboard-info.com/EndorsementSearch.wsdl"

xmlns:esxsd="http://schemas.snowboard-info.com/EndorsementSearch.xsd"

Figure 1-8. Image from the W3C SOAP spec page

17

See http://www.w3.org/2001/03/14-annotated-WSDL-examples.

CHAPTER 1 REST 101

33

xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"

xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/">

<!-- wsdl:types encapsulates schema definitions of communication types;

here using xsd -->

<wsdl:types>

<xsd:schema targetNamespace="http://namespaces.snowboard-info.com"

xmlns:xsd="http://www.w3.org/1999/XMLSchema">

<!-- xsd definition: GetEndorsingBoarder [manufacturer string, model

string] -->

<xsd:element name="GetEndorsingBoarder">

<xsd:complexType>

<xsd:sequence>

<xsd:element name="manufacturer" type="string"/>

<xsd:element name="model" type="string"/>

</xsd:sequence>

</xsd:complexType>

</xsd:element>

<!-- xsd definition: GetEndorsingBoarderResponse [... endorsingBoarder

string ...] -->

<xsd:element name="GetEndorsingBoarderResponse">

<xsd:complexType>

<xsd:all>

<xsd:element name="endorsingBoarder" type="string"/>

</xsd:all>

</xsd:complexType>

</xsd:element>

<!-- xsd definition: GetEndorsingBoarderFault [... errorMessage

string ...] -->

<xsd:element name="GetEndorsingBoarderFault">

<xsd:complexType>

<xsd:all>

<xsd:element name="errorMessage" type="string"/>

CHAPTER 1 REST 101

34

</xsd:all>

</xsd:complexType>

</xsd:element>

</xsd:schema>

</wsdl:types>

<wsdl:message name="GetEndorsingBoarderRequest">

<wsdl:part name="body" element="esxsd:GetEndorsingBoarder"/>

</wsdl:message>

<!-- response GetEndorsingBoarderResponse is of type GetEndorsingBoarder

Response -->

<wsdl:message name="GetEndorsingBoarderResponse">

<wsdl:part name="body" element="esxsd:GetEndorsingBoarderResponse"/>

</wsdl:message>

<wsdl:portType name="GetEndorsingBoarderPortType">

<wsdl:operation name="GetEndorsingBoarder">

<wsdl:input message="es:GetEndorsingBoarderRequest"/>

<wsdl:output message="es:GetEndorsingBoarderResponse"/>

<wsdl:fault message="es:GetEndorsingBoarderFault"/>

</wsdl:operation>

</wsdl:portType>

<wsdl:binding name="EndorsementSearchSoapBinding"

type="es:GetEndorsingBoarderPortType">

<!-- leverage off soap:binding document style @@@(no wsdl:foo pointing

at the soap binding) -->

<soap:binding style="document"

transport="http://schemas.xmlsoap.org/soap/http"/>

CHAPTER 1 REST 101

35

<!-- semi-opaque container of network transport details classed by

soap:binding above @@@ -->

<wsdl:operation name="GetEndorsingBoarder">

<soap:operation soapAction="http://www.snowboard-info.com/

EndorsementSearch"/>

<!-- furthur specify that the messages in the wsdl:operation

"GetEndorsingBoarder" use SOAP? @@@ -->

<wsdl:input>

<soap:body use="literal"

namespace="http://schemas.snowboard-info.com/

EndorsementSearch.xsd"/>

</wsdl:input>

<wsdl:output>

<soap:body use="literal"

namespace="http://schemas.snowboard-info.com/

EndorsementSearch.xsd"/>

</wsdl:output>

<wsdl:fault>

<soap:body use="literal"

namespace="http://schemas.snowboard-info.com/

EndorsementSearch.xsd"/>

</wsdl:fault>

</wsdl:operation>

</wsdl:binding>

<wsdl:service name="EndorsementSearchService">

<wsdl:documentation>snowboarding-info.com Endorsement Service</wsdl:

documentation>

<wsdl:port name="GetEndorsingBoarderPort"

binding="es:EndorsementSearchSoapBinding">

CHAPTER 1 REST 101

36

<soap:address location="http://www.snowboard-info.com/

EndorsementSearch"/>

</wsdl:port>

</wsdl:service>

</wsdl:definitions>

The main drawback of these types of services was the amount of information used,

both to describe them and to use them. Even though XML provided the much-required

technology agnostic means of encoding data to be transmitted between two systems, it

also blotted the message sent quite noticeably.

Both of these technologies (XML-RPC and SOAP + WSDL) provided the solution to

system interconnectivity at a time when it was required. They provided a way to transmit

messages using a “universal” language between all systems, but they also had several

major issues compared to today’s leading standard (see Table1-4). This can be clearly

seen, for example, in the way developers feel about using XML instead of JSON.

Table 1-4. Comparison of XML-RPC/SOAP and REST Services

XML-RCP/SOAP REST

Specic SOAP clients had to be created for each

programming language. Even though XML was

universal, a new client would have to be coded to parse

the WSDL to understand how the service worked.

REST is completely technology-agnostic

and doesn’t require special clients, only

a programming language capable of

connectivity through the chosen protocol

(e.g., HTTP, FTP, etc.).

The client needs to know everything about the service

before initiating the interaction (thus the WSDL

mentioned earlier).

The client only needs to know the main

root endpoint, and with the hypermedia

provided on the response, self-discovery is

possible.

Because the service was used from within the client

source code and called a specic function or method

from within the server’s code, the coupling between

those two systems was too big. A rewrite of the server

code would probably lead to a rewrite on the client’s

code.

The interface is implementation-

independent; the complete server-side

code can be rewritten and the API’s

interface will not have to be changed.

CHAPTER 1 REST 101

37

Note Comparing XML-RPC/SOAP with REST might not be entirely fair (or possible)

due to the fact that the first two are protocols, whereas the latter is an architectural

style; but some points can still be compared if you keep that distinction in mind.

Summary

This chapter was a small overview of what REST is meant to be and the kind of benefits

a system will gain by following the REST style. The chapter also covered a few extra

principles, like HTTP verbs and status codes, which despite not being part of the REST

style, are indeed part of the HTTP standard, the protocol we’re basing this book on.

Finally, I discussed the main technologies used prior to REST, and you saw how they

compared to the current leading industry standard.

In the next chapter, I’ll go over some good API design practices, and you’ll see how

you can achieve them using REST.

CHAPTER 1 REST 101

39

F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1_2

CHAPTER 2

API Design Best Practices

The practice of API design is a tricky one. Even when there are so many options out

there—tools to use, standards to apply, styles to follow—there is one basic question that

needs to be answered and needs to be clear in the developer’s mind before any kind

design and development can begin…

What Defines aGood API?

As we all know, the concepts of “good” and “bad” are very subjective (one could

probably read a couple of books discussing this on its own), and therefore, opinions vary

from one person to another. That being said, years of experience of dealing with different

kinds of APIs have left the developer community (and this author) with a pretty good

sense of the need-to-have features of any good API. (Disclaimer: Things like clean code,

good development practices, and other internal considerations will not be mentioned

here but will be assumed, since they should be part of every software undertaking.)

So let’s go over this list.

• Developer-friendly: The developers working with your API should not

suffer when dealing with your system.

• Extensibility: Your system should be able to handle the addition of

new features without breaking your clients.

• Up-to-date documentation: Good documentation is key to your API

being picked up by new developers.

• Proper error handling: Because things will go wrong and you need to

be prepared.

• Provides multiple SDK/libraries: e more work you simplify for

developers, the more they’ll like your system.

40

• Security: A key aspect of any global system.

• Scalability: The ability to scale up and down is something any good

API should have to properly provide its services.

I’ll go over these points one by one and show how they affect the API and how

following the REST style help.

Developer-Friendly

By definition, an API is an application programming interface, with the key word

being interface. When thinking about designing an API that will be used by developers

other than yourself, there is a key aspect that needs to be taken into consideration: the

Developer eXperience (or DX).

Even when the API will be used by another system, the integration into that system

is first done by one or more developers—human beings that bring the human factor

into that integration. This means you’ll want the API to be as easy to use as possible,

which makes for a great DX, and which should translate into more developers and client

applications using the API.

There is a trade-off, though, since simplifying things for humans could lead into

an oversimplification of the interface, which in turn could lead to design issues when

dealing with complex functionalities.

It is important to consider the DX as one of the major aspects of an API (let’s be

honest, without developers using it, there is no point to an API), but there are other

aspects that have to be considered and given weight in the design decisions. Make it

simple, but not dummy simple.

The next sections provide some pointers for a good DX.

Communication’s Protocol

This is one of the most basic aspects of the interface. When choosing a communication

protocol, it’s always a good idea to go with one that is familiar to the developers using

the API.There are several standards that already have libraries and modules available in

many programming languages (e.g., HTTP, FTP, SSH, etc.).

A custom-made protocol isn’t always a good idea because you’ll lose that instant

portability in so many existing technologies. That said, if you’re ready to create support

CHAPTER 2 API DESIGN BEST PRACTICES

41

libraries for the most used languages, and your custom protocol is more efficient for your

use case, it could be the right choice.

In the end, it’s up to the API designer to evaluate the best solution based on the

context in which he’s working.

In this book, you’re working under the assumption that the protocol chosen for REST

is HTTP.

1

It’s a very well-known protocol; any modern programming language supports

it and it’s the basis for the entire Internet. You can rest assured that most developers have

a basic understanding of how to use it. And if not, there is plenty of information out there

to get to know it better.

In summary, there is no silver bullet protocol out there perfect for every scenario.

Think about your API needs, make sure that whatever you choose is compatible with

REST, and you’ll be fine.

Easy-to-Remember Access Points

The points of contact between all client apps and the API are called endpoints. The API

needs to provide them to allow clients to access its functionalities. This can be done

through whatever communications protocol is chosen. These access points should have

mnemotechnic names to help the developer understand their purpose just by reading them.

Of course, the name by itself should never be a replacement for a detailed documentation,

but it is normally considered a good idea to reference the resource being used and to have

some kind of indicator of the action being taken when calling that access point.

The following is a good example of a badly named access point (meant to list the

books in a bookstore):

GET /books/action1

This example uses the HTTP protocol to specify the access point, and even though

the entity used (books) is being referenced, the action name is not clear; action1 could

mean anything, or even worse, the meaning could change in the future, but the name

would still be suitable, so any existing client would undoubtedly break.

A better example—one that follows REST and the standards discussed in

Chapter 1—would be this:

GET /books

1

See http://www.w3.org/Protocols/rfc2616/rfc2616.html.

CHAPTER 2 API DESIGN BEST PRACTICES

42

This should present the developer with more than enough information to

understand that a GET request into the root of a resource (/books) will always yield a list

of items of this type; then the developer can replicate this pattern into other resources, as

long as the interface is kept uniform across all other endpoints.

Uniform Interface

Easy-to-remember access points are important, but so is being consistent when defining

them. Again, you have to go back to the human factor when consuming an API: you’re

a human too. So making the lives of the developers using your APIs easier is a must if

you want anyone to use it, you can’t forget about the DX.That means you need to be

consistent when defining endpoints’ names, request formats, and response formats.

There can be more than one version for the latter two (more specifically, the response

format is directly tied to the various representations a resource can have), but as long as

the default is always the same, there will be no problems.

A good example of an inconsistent interface, even though not on an API, can be

seen in the programming language PHP.It has underscore notation on most functions’

names, but the underscore is not used on some, so the developer is always forced to go

back to the documentation to check how to write these functions (or worse, rely on

his/her memory).

For example, str_replace is a function that uses an underscore to separate both

words (str and replace), whereas htmlentities has no separation of words at all.

Another example of bad design practice in an API is to name the endpoints based on

the actions taken instead of the resources handled; for example:

/getAllBooks

/submitNewBook

/updateAuthor

/getBooksAuthors

/getNumberOfBooksOnStock

These examples clearly show the pattern that this API is following. And at first glance,

they might not seem that bad, but consider how poor the interface is going to become

as new features and resources are added to the system (not to mention if the actions are

modified). Each new addition to the system causes extra endpoints to the API’s interface.

The developers of client apps will have no clue as to how these new endpoints are

CHAPTER 2 API DESIGN BEST PRACTICES

43

named. For instance, if the API is extended to support the cover images of books, with

the current naming scheme, these are all possible new endpoints:

/addNewImageToBook

/getBooksImages

/addCoverImage

/listBooksCovers

And the list can go on. So for any real-world application, you can safely assume

that following this type of pattern will yield a really big list of endpoints, increasing the

complexity of both server-side code and client-side code. It will also hurt the system’s

ability to capture new developers, due to the inherited complexity that it will have over

the years.

To solve this problem and generate an easy-to-use and uniform interface across

the entire API, you can apply the REST style to the endpoints. If you remember the

constraints proposed by REST from Chapter 1, you end up with a resource-centric

interface. And thanks to HTTP, you also have verbs to indicate actions.

Table2-1 shows how the previous interface changes using REST.

Table 2-1. List of Endpoints and How They Change When the REST Style Is

Applied

Old Style REST Style

/getAllBooks GET /books

/submitNewBook POST /books

/updateAuthor PUT /authors/:id

/getBooksAuthors GET /books/:id/authors

/getNumberOfBooksOnStock GET /books (This number can easily be returned as part of this endpoint.)

/addNewImageToBook PUT /books/:id

/getBooksImages GET /books/:id/images

/addCoverImage POST /books/:id/cover_image

/listBooksCovers GET /books (This information can be returned in this endpoint using

subresources.)

CHAPTER 2 API DESIGN BEST PRACTICES

44

You went from having to remember nine different endpoints to just two, with the

added bonus of having all HTTP verbs being the same in all cases once you defined the

standard; now there is no need to remember specific roles in each case (they’ll always

mean the same thing).

Transport Language

Another aspect of the interface to consider is the transport language used. For many

years, the de facto standard was XML; it provided a technology-agnostic way of

expressing data that could easily be sent between clients and servers. Nowadays, there is

a new standard gaining popularity over XML—JSON.

Why JSON?

JSON has been gaining traction over the past few years (see Figure2-1) as the standard

Data Transfer Format. This is mainly due to the advantages that it provides. The

following lists just a few:

• It’s lightweight. There are very little data in a JSON file that are not

directly related to the information being transferred. This is a major

winning point over more verbose formats like XML.

2

• It’s human-readable. e format itself is so simple that it can easily

be read and written by a human. is is particularly important

considering that a focus point of the interface of any good API is the

human factor (otherwise known as the DX).

• It supports dierent data types. Because not everything being

transferred is a string, this feature allows the developer to provide

extra meaning to the information transferred.

2

XML is not strictly a Data Transfer Format, but it’s being used as one.

CHAPTER 2 API DESIGN BEST PRACTICES

45

The list could go on, but these are the three main aspects that are helping JSON win

so many followers in the developer community.

Even though JSON is a great format and is gaining traction, it’s not the silver bullet

that will always solve all of your problems, so it’s also important to provide clients with

options. And here is where REST comes to help.

Since the protocol you’re basing REST on is HTTP, developers can use a mechanism

called content negotiation to allow clients to specify which of the supported formats they

want to receive (as discussed in Chapter 1). This allows for more flexibility on the API

and still keeps the interface uniform.

Going back to the list of endpoints, the last one talks about using a subresource as

the solution. That can be interpreted in several ways, because not only is the language

used to transfer the data important, but so is the structure that you give the data being

transferred. My final advice for a uniform interface is to standardize the format used, or

even better, follow an existing one, like Hypertext Application Language (HAL).

This was covered in Chapter 1, so refer back to it for more information.

Figure 2-1. Trend of Google searches for “JSON” vs. “XML” over the last few

years

CHAPTER 2 API DESIGN BEST PRACTICES

46

Extensibility

A good API is never fully finished. This might be a bold claim, but it’s one that comes

from the experience of the community. Let’s look at some of the big ones.

3

• Google APIs: 5 billion calls a day;

4

launched in 2005

• Facebook APIs: 5 billion calls a day;

5

launched in 2007

• Twitter APIs: 13 billion calls a day;

6

launched in 2006

These examples show that even when a great team is behind the API, the APIs will

keep growing and changing because the client apps developers find new ways to use it,

the business model of the API owner changes over time, or simply because features are

added and removed.

When any of this happens, the API may need to be extended or changed, and new

access points added or old ones changed. If the original design is right, then going from v1 to

v2 should be no problem, but if it’s not, then that migration could spell disaster for everyone.

How Is Extensibility Managed?

When extending the API, you’re basically releasing a new version of your software, so the

first thing you need to do is let your users (the developers) know what will happen once

the new version is out. Will their apps still work? Are the changes backward-compatible?

Will you maintain several versions of your API online or just the latest one?

A good API should take the following points into consideration:

• How easily can new endpoints be added?

• Is the new version backward-compatible?

• Can clients continue to work with older versions of the API while

their code is being updated?

• What will happen to existing clients targeting the new API?

3

Source: http://www.slideshare.net/3scale/apis-for-biz-dev-20-which-business-model-15473323.

4

Source: http://www.slideshare.net/3scale/apis-for-biz-dev-20-which-business-model-15473323,

April 2010.

5

Source: http://www.slideshare.net/3scale/apis-for-biz-dev-20-which-business-model-15473323,

October 2009.

6

Source: http://www.slideshare.net/3scale/apis-for-biz-dev-20-which-business-model-15473323,

May 2011.

CHAPTER 2 API DESIGN BEST PRACTICES

47

• How easy will it be for clients to target the new version of the API?

Once all these points are settled, then you can safely grow and extend the API.

Normally, going from version A to version B of an API by instantly deprecating

version A and taking it offline in favor of version B is considered a bad move, unless, of

course, you have very few client applications using that version.

A better approach for this type of situation is to allow developers to choose which

version of the API they want to use, keeping the old version long enough to let everyone

migrate into the newer one. And to do this, an API would include its version number in

the resource identifier (i.e., the URL of each resource). This approach makes the version

number a mandatory part of the URL to clearly show the version in use.

Another approach, which may not be as clear, is to provide a versionless URL that

points to the latest version of the API and an optional URL parameter to overwrite the

version. Both approaches have pros and cons that have to be weighted by the developer

creating the API. Tables 2-2 and 2-3 show the pros and cons of both options.

Table 2-2. Pros and Cons of Having the Version of the API As Part of the URL

Pros Cons

The version number is clearly visible, helping

prevent confusion about the version being used.

URLs are more verbose.

Easy to migrate from one version to another, from

a client perspective (all URLs change the same

portion—the version number )

A wrong implementation on the API code

could cause a huge amount of work when

migrating from one version to the other (i.e.,

if the version is hardcoded on the endpoint’s

URL template, individually for every endpoint).

Allows cleaner architecture when more than one

version of the API needs to be kept working

Clear and simple migration from one version to the

next from the API perspective, since both versions

could be kept working in parallel for a period of time,

allowing slower clients to migrate without breaking

The right versioning scheme can make xes and

backward-compatible new features instantly available

without the need to update on the client’s part.

CHAPTER 2 API DESIGN BEST PRACTICES

48

Keeping this in mind, there are several versioning schemes to use when it comes to

setting the version of a software product:

• Ubuntu’s

7

version numbers represent the year and month of the

release; so version 14.04 means it was released in April 2014.

• In the Chromium project, version numbers have four parts:

8

MAJOR.

MINOR.BUILD.PATCH.The following is from the Chromium

project’s page on versioning: MAJOR and MINOR may get updated

with any significant Google Chrome release (Beta or Stable update).

MAJOR must get updated for any backward-incompatible user data

change (since this data survives updates). BUILD must get updated

whenever a release candidate is built from the current trunk (at least

weekly for Dev channel release candidates). The BUILD number

is an ever-increasing number representing a point in time of the

Chromium trunk. PATCH must get updated whenever a release

candidate is built from the BUILD branch.

7

See https://help.ubuntu.com/community/CommonQuestions#Ubuntu_Releases_and_Version_Numbers.

8

See http://www.chromium.org/developers/version-numbers.

Table 2-3. Pros and Cons of Having the API Version Hidden from the User

Pros Cons

Simpler URLs A Hidden version number might lead to

confusion about the version being used.

Instant migration to latest working code of

the API

Non-backward-compatible changes will break

the clients that are not referencing a specic

version of the API.

Simple migration from one version to the next

from the client’s perspective (only change the

value of the attribute)

Complex architecture required to make version

selection available

Easy test of client code against the latest version

(just don’t send version-specic parameters)

CHAPTER 2 API DESIGN BEST PRACTICES

49

• Another intermediate approach, known as Semantic Versioning or

SemVer,

9

is well accepted by the development community. It provides

the right amount of information. It has three numbers for each

version: MAJOR.MINOR.PATCH.

• MAJOR represents changes that are not backward-compatible.

• MINOR represents new features that leave the API backward-

compatible.

• PATCH represents small changes like bug fixes and code

optimization.

With that scheme, the first number is the only one that is really relevant to clients,

since that’ll be the one indicating compatibility with their current version.

By having the latest version of MINOR and PATCH deployed on the API at all times,

you’re providing clients with the latest compatible features and bug fixes, without

making clients update their code.

So with that simple versioning scheme, the endpoints look like this:

GET /1/books?limit=10&size=10

POST /v2/photos

GET /books?v=1

When choosing a versioning scheme, please take the following into consideration:

• Using the wrong versioning scheme might cause confusion or

problems when implementing a client app by consuming the wrong

version of the API.For instance, using Ubuntu’s versioning scheme

for your API might not be the best way to communicate what is going

on in each new version.

• e wrong versioning scheme might force clients to update a lot,

like when a minor x is deployed or a new backward-compatible

feature is added. ose changes shouldn’t require a client update. So

don’t force the client to specify those parts of the version unless your

scheme requires it.

9

See semver.org.

CHAPTER 2 API DESIGN BEST PRACTICES

50

Up-to-Date Documentation

No matter how mnemotechnic your endpoints are, you still need to have documentation

explaining everything that your API does. Whether optional parameters or the

mechanics of an access point, the documentation is fundamental to having a good DX,

which translates into more users.

A good API requires more than just a few lines explaining how to use an access point

(there is nothing worse than discovering that you need an access point but it has no

documentation at all) but needs a full list of parameters and explanatory examples.

Some providers give developers a simple web interface to try their API without

having to write any code. This is particularly useful for newcomers.

There are some online services that allow API developers to upload their

documentation, as well as those that provide the web UI to test the API; for example,

Mashape provides this service for free (see Figure2-2).

Figure 2-2. The service provided by Mashape

CHAPTER 2 API DESIGN BEST PRACTICES

51

Another good example of detailed documentation is at Facebook’s developer site.

10

It provides implementation and usage examples for all the platforms that Facebook

supports (see Figure2-3).

An example of a poorly written documentation is seen in Figure2-4. It is 4chan’s API

documentation.

11

Yes, the API appears to not be complicated enough to merit writing a whole book

about it, but then again, there are no examples provided, only a generic explanation of

how to find the endpoints and what parameters to use.

Newcomers might find it hard to understand how to implement a simple client that

uses this API.

10

See https://developers.facebook.com/docs/graph-api/using-graph-api/v2.1.

11

See https://github.com/4chan/4chan-API.

Figure 2-3. Facebook’s API documentation site

CHAPTER 2 API DESIGN BEST PRACTICES

52

Note It’s unfair to compare 4chan’s documentation to that of Facebook’s, since

the size of the teams and companies are completely different. But you should note

the lack of quality in 4chan’s documentation.

Although it might not seem like the most productive idea while developing an API,

the team needs to consider working on extensive documentation. It is one of the main

things that will assure the success or failure of the API for two main reasons:

• It should help newcomers and advance developers to consume your

API without any problems.

• It should serve as a blueprint for the development team, if it is kept up-to-

date. Jumping into a project mid-development is easier if there is a well-

written and well-explained blueprint of how the API is meant to work.

Figure 2-4. Introduction to 4chan’s API documentation

CHAPTER 2 API DESIGN BEST PRACTICES

53

Note This also applies to updating the documentation when changes are made

to the API.You need to keep it updated; otherwise, the effect is the same as not

having documentation at all.

Proper Error Handling

Error handling on an API is incredibly important, because if it is done right, it can help

the client app understand how to handle errors; and on the human side (the DX), it can

help developers understand what it is they’re doing wrong and how to fix it.

There are two very distinct moments during the life cycle of an API client that you

need to consider error handling:

• Phase 1: The development of the client

• Phase 2: e client is implemented and being used by end users.

Phase 1: Development oftheClient

During the first phase, developers implement the required code to consume the API.

It is very likely that a developer will have errors on the requests (things like missing

parameters, wrong endpoint names, etc.) during this stage.

Those errors need to be handled properly, which means returning enough

information to let developers know what they did wrong and how they can fix it.

CHAPTER 2 API DESIGN BEST PRACTICES

54

A common problem with some systems is that their creators ignore this stage, and

when there is a problem with the request, the API crashes, and the returned information

is just an error message with the stack trace and the status code 500, as seen in Figure2-5.

The response in Figure2-5 shows what happens when you forget to add error

handling in the client development stage. The stack trace returned might give the

developer some sort of clue (at best) as to what exactly went wrong, but it also shows

a lot of unnecessary information, so it ends up being confusing. This certainly hurts

development time, and no doubt would be a major point against the DX of the API.

Figure 2-5. A classic example of a crash on the API returning the stack trace

CHAPTER 2 API DESIGN BEST PRACTICES

55

On the other hand, let’s take a look at a proper error response for the same error in

Figure2-6.

Figure2-6 clearly shows that there has been an error, what the error is, and an error

code. The response only has three attributes, but they’re all helpful:

• The error indicator gives the developer a clear way to check whether

or not the response is an error message (you could also check against

the status code of the response).

• e error message is clearly intended for the developer and not only

states what’s missing, but also explains how to x it.

• A custom error code, if explained in the documentation, could help

a developer automate actions when this type of response happens

again.

Phase 2: TheClient Is Implemented andBeing Used

byEnd Users

During this stage in the life cycle of the client, you’re not expecting any more developer

errors, such as using the wrong endpoint, missing parameters, and the like, but there

could still be problems caused by the data generated by the user.

Client applications that request some kind of input from the user are always subject

to errors on the user’s part, and even though there are always ways to validate that input

before it reaches the API layer, it’s not safe to assume all clients will do that. So the safest

bet for any API designer and developer is to assume there is no validation done by the

Figure 2-6. A proper error response would look like this

CHAPTER 2 API DESIGN BEST PRACTICES

56

client, and anything that could go wrong with the data will go wrong. This is also a safe

assumption to make from a security point of view, so it’s providing a minor security

improvement as a side effect.

With that mindset, the API implemented should be rock-solid and able to handle any

type of errors in the input data.

The response should mimic that from phase 1: there should be an error indicator, an

error message stating what’s wrong (and, if possible, how to fix it), and a custom error

code. The custom error code is especially useful in this stage, since it’ll provide the client

with the ability to customize the error shown to the end user (even showing a different

but still relevant error message).

Multiple SDK / Libraries

If you expect your API to be massively used across different technologies and platforms,

it might be a good idea to develop and provide support for libraries and SDKs that can be

used with your system.

By doing so, you provide developers with the means to consume your services, so

all they have to do is use these services to create their client apps. Essentially, you’re

shaving off potential weeks or months (depending on the size of your system) of

development time.

Another benefit is that most developers will inherently trust your libraries over

others that do the same, because you’re the owner of the service those libraries are

consuming.

Finally, consider open sourcing the code of your libraries. These days, the open

source community is thriving. Developers will undoubtedly help maintain and improve

your libraries if they’re of use to them.

Let’s look again at some of the biggest APIs out there:

• Facebook API provides SDKs for iOS, Android, JavaScript, PHP, and

Unity.

12

• Google Maps API provides SDKs for several technologies, including

iOS, the Web, and Android.

13

12

See https://developers.facebook.com (see the bottom of the page for the list of SDKs).

13

See https://developers.google.com/maps/.

CHAPTER 2 API DESIGN BEST PRACTICES

57

• Twitter API provides SDKs for several of their APIs, including Java,

ASP, C++, Clojure, .NET, Go, JavaScript, and a lot of other languages.

14

• Amazon provides SDKs for their AWS service, including PHP, Ruby,

.NET, and iOS.ey even have those SDKs on GitHub for anyone

to see.

15

Security

Securing your API is a very important step in the development process, and it should

not be ignored, unless what you’re building is small enough and has no sensitive data to

merit the effort.

There are two big security issues to deal with when designing an API:

• Authentication: Who’s going to access the API?

• Authorization: What will they be able to access once logged in?

Authentication deals with letting valid users access the features provided by the

API.Authorization deals with handling what those authenticated users can actually do

inside the system.

Before going into details about each specific issue, there are some common aspects

that need to be remembered when dealing with security on RESTful systems (at least,

those based on HTTP):

• RESTful systems are meant to be stateless: Remember that REST

defines the server as stateless, which means that storing the user data

in session after the initial login is not a good idea (if you want to stay

within the guidelines provided by REST, that is).

• Remember to use HTTPS: On RESTful systems based on HTTP,

HTTPS should be used to assure encryption of the channel, making it

harder to capture and read data trac (man-in-the-middle attack).

14

See https://dev.twitter.com/overview/api/twitter-libraries.

15

See https://github.com/aws.

CHAPTER 2 API DESIGN BEST PRACTICES

58

Accessing theSystem

There are some widely used authentication schemes out there meant to provide different

levels of security when signing users into a system. Some of the most commonly known

are Basic Auth with TSL, Digest Auth, OAuth 1.0a, and OAuth 2.0.

I’ll go over these and talk about each of their pros and cons. I’ll also cover an

alternative method that should prove to be the most RESTful, in the sense that it’s 100%

stateless.

Almost Stateless Methods

OAuth 1.0a, OAuth 2.0, Digest Auth, and Basic Auth + TSL are the go-to methods of

authentication these days. They work wonderfully, they have been implemented in all of

the modern programming languages, and they have proven to be the right choice for the

job (when used for the right use-case). That being said, as you’re about to see, none of

them are 100% stateless.

They all depend on having the user have information stored on some kind of cache

layer on the server side. This little detail, especially for the purists out there, means a

no-go when designing a RESTful system, because it goes against one of the most basic

of the constraints imposed by REST: Communication between client and server must be

stateless.

This means the state of the user should not be stored anywhere.

You will look the other way in this particular case, however. I’ll cover the basics of

each method anyway, because in real life, you have to compromise and you have to find

a balance between purism and practicality. But don’t worry. I’ll go over an alternative

design that will solve authentication and stay true to REST.

Basic Auth withTSL

Thanks to the fact that you’re basing REST on HTTP for the purpose of this book, the

latter provides a basic authentication method that most of the languages can support.

Keep in mind, though, that this method is aptly named, since it’s quite basic and

works by sending the username and password unencrypted over HTTP.So the only way

to make it secure is to use it with a secured connection over HTTPS (HTTP + TSL).

This authentication method works as follows (see Figure2-7):

CHAPTER 2 API DESIGN BEST PRACTICES

59

1. First, a client makes a request for a resource without any special

header.

2. e server responds with a 401 unauthorized response, and within

it, a WWW-Authenticate header, specifying the method to use

(Basic or Digest) and the realm name.

3. The client then sends the same request but adds the Authorization

header, with the string USERNAME:PASSWORD encoded in base 64.

On the server side, there needs to be some code to decode the authentication string

and load the user data from the session storage used (normally a database).

Aside from the fact that this approach is one of the many that will break the

nonstateless constraint, it’s easy and fast to implement.

Note When using this method, if the password for a logged in user is reset,

then the login data sent on the request becomes old and the current session is

terminated.

Figure 2-7. The steps between client and server on Basic Auth

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60

Digest Auth

This method is an improvement over the previous one, in the sense that it adds an extra

layer of security by encrypting the login information. The communication with the

server works the same way, by sending the same headers back and forth.

With this methodology, upon receiving a request for a protected resource, the server

will respond with a WWW-Authenticate header and some specific parameters. Here are

some of the most interesting:

• Nounce: A uniquely generated string. This string needs to be unique

on every 401 response.

• Opaque: A string returned by the server that has to be sent back by

the client unaltered

• Qop: Even though optional, this parameter should be sent to specify

the quality of protection needed (more than one token can be sent in

this value). Sending auth back would imply a simple authentication,

whereas sending auth-int implies authentication with integrity

check.

• Algorithm: This string specifies the algorithm used to calculate the

checksum response from the client. If not present, then MD5 should

be assumed.

For the full list of parameters and implementation details, please refer to the RFC.

16

Here is a list of some of the most interesting ones:

• Username: The unencrypted username.

• URI: e URI you’re trying to access.

• Response: e encrypted portion of the response. is proves that you

are who you say you are.

• Qop: If present, it should be one of the supported values sent by the

server.

16

See https://www.ietf.org/rfc/rfc2617.txt.

CHAPTER 2 API DESIGN BEST PRACTICES

61

To calculate the response, the following logic needs to be applied:

MD5(HA1:STRING:HA2)

Those values for HA1 are calculated as follows:

• If no algorithm is specified on the response, then

MD5(username:realm:password) should be used.

• If the algorithm is MD5-less, then it should be

MD5(MD5(username:realm:password):nonce:cnonce)

Those values for HA2 are calculated as follows:

• If qop is auth, then MD5(method:digestURI) should be used.

• If qop is auth-int, then MD5(method:digestURI:MD5(entityBody))

should be used.

Finally, the response will be as follows:

MD5(HA1:nonce:nonceCount:clientNonce:HA2) //for the case when "qop" is

"auth" or "auth-int"

MD5(HA1:nonce:HA2) //when "qop" is unspecified.

The main issue with this method is that the encryption used is based on MD5, and

in 2004 it was proven that this algorithm is not collision-resistant, which basically means

a man-in-the-middle attack would make it possible for an attacker to get the necessary

information and generate a set of valid credentials.

A possible improvement over this method, just like with its “Basic” brother, would be

adding TSL; this would definitely help make it more secure.

CHAPTER 2 API DESIGN BEST PRACTICES

62

OAuth 1.0a

OAuth 1.0a is the most secure of the four nonstateless methodologies described

in this section. The process is a bit more tedious than the ones described earlier

(see Figure2-8), but the trade-off here is a significantly increased level of security.

In this case, the service provider has to allow the developer of the client app

to register the app on the provider’s web site. By doing so, the developer obtains a

consumer key (a unique identifying key for his application) and the consumer secret.

Once that process is done, the following steps are required:

1. e client app needs a request token. e purpose is to receive

the user’s approval and then request an access token. To get the

request token, a specic URL must be provided by the server; in

this step, the consumer key and the consumer secret are used.

2. Once the request token is obtained, the client must make a

request using the token on a specic server URL (i.e., http://

provider.com/oauth/authorize) to get authorization from the

end user.

3. After authorization from the user is given, then the client app

makes a request to the provider for an access token and a token

secret key.

4. Once the access token and secret token are obtained, the client

app is able to request protected resources for the provider on

behalf of the user by signing each request.

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63

Figure 2-8. The interaction between client and server

CHAPTER 2 API DESIGN BEST PRACTICES

64

For more details on how this method works, please refer to the complete

documentation.

17

OAuth 2.0

OAuth 2.0 is meant to be the evolution of OAuth 1.0a; it focuses on client developer

simplicity. The main problem with implementations of systems that worked with

OAuth 1.0 was the complexity implied in the last step: signing every request.

Due to its complexity, the last step is the key weak point of the algorithm: if either the

client or server makes a tiny mistake, then the requests will not validate. Even when the

same aspect made it the only methodology that didn’t need to work on top of SSL

(or TSL), this benefit wasn’t enough.

OAuth 2.0 tries to simplify the last step by making some key changes, mainly:

• It relies on SSL (or TSL) to ensure that the information sent back and

forth is encrypted.

• Signatures are not required for requests after the token has been

generated.

To summarize, this version of OAuth tries to simplify the complexity introduced by

OAuth 1.0, while sacrificing security at the same time (by relying on TSL to ensure data

encryption). It is the preferred method over OAuth 1.0 if the devices you’re dealing with

have support for TSL (computers, mobile devices, etc.); otherwise, you might want to

consider using other options.

A Stateless Alternative

As you’ve seen, the alternatives you have when it comes to implementing a security

protocol to allow users to sign into a RESTful API are not stateless, and even though you

should be prepared to make that commitment to gain the benefits of tried and tested

ways of securing your application, there is a fully REST compatible way of doing it as well.

If you go back to Chapter 1, the stateless constraints basically imply that any and

all states of the communication between client and server should be included on every

request made by the client. This of course includes the user information, so if you want

to have stateless authentication, then you need to include that in your requests as well.

17

See http://oauth.net/core/1.0a/.

CHAPTER 2 API DESIGN BEST PRACTICES

65

If you want to ensure the authenticity of each request, you can borrow the signature

step of OAuth 1.0a and apply it on every request by using a pre-established secret key

between the client and the server and a MAC (Message Authentication Code) algorithm

to do the signing (see Figure2-9).

As you’re keeping it stateless, the information required to generate the MAC needs to

also be sent as part of the request, so the server can re-create the result and corroborate

its validity.

This approach has some clear advantages in our case, mainly:

• It’s simpler than both OAuth 1.0a and OAuth 2.0.

• Zero storage is needed, since any and all required information to

validate the encryption needs to be sent on every request.

Figure 2-9. How the MAC signing process works

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66

Scalability

Last but certainly not least is scalability.

Scalability is usually an underestimated aspect of API design, mainly because

it’s quite difficult to fully understand and predict the reach one API will have before

it launches. It might be easier to estimate this if the team has previous experience

with similar projects (e.g., Google has probably gotten quite good at calculating their

scalability for new APIs before launch day), but if it’s their first one, then it might not be

as easy.

A good API should be able to scale—that means it should be able to handle as much

traffic as it gets without compromising its performance. But it also means it should not

spend resources if they’re not needed. This is not only a reflection of the hardware on

which the API resides (although that is an important aspect), but also a reflection of the

underlying architecture of that API.

Over the years, the classic monolithic design in software architecture has been

migrating into a fully distributed one, so splitting the API into different modules that

interact with each other makes sense.

This provides the flexibility needed to not only scale up or down the resources that

are affected but to also provide fault tolerance and help developers maintain cleaner

code bases among other advantages.

The following image (Figure2-10) shows a standard monolithic design, having your

app inside one server, living like one single entity.

CHAPTER 2 API DESIGN BEST PRACTICES

67

Figure 2-10. Simple diagram of a monolithic architecture

CHAPTER 2 API DESIGN BEST PRACTICES

68

In Figure2-11 you see a distributed design. If compared with Figure2-10, you can

see where the advantages come from (better resource usage, fault tolerance, easier to

scale up or down, etc.).

Figure 2-11. A diagram showing an example of a distributed architecture

CHAPTER 2 API DESIGN BEST PRACTICES

69

Achieving a distributed architecture to ensure scalability using REST is quite simple.

Fielding’s paper proposes a distributed system based on a client–server scheme.

So splitting the entire system into a set of smaller APIs and having them talk to each

other when required will ensure the advantages mentioned earlier.

For instance, let’s look at an internal system for a bookstore (Table2-4).

Table 2-4. List of Entities and Their Role Inside the System

Entity Description

Books Represents the inventory of the store. It’ll control everything from book data, to number

of copies, and so forth.

Clients Contact information of clients

Users Internal bookstore users; they will have access to the system

Purchases Records information about book sales

Now, consider that system on a small bookstore, one that is just starting and has just

a few employees. It’s very tempting to go with a monolithic design; not a lot of resources

will be spent and the design is quite simple.

Now, consider what would happen if the small bookstore suddenly grows so much

that it expands into several other bookstores. They go from having 1 store to 100,

employee numbers grow, books need better tracking, and purchases skyrocket.

The simple system from before will not be enough to handle such growth. It would

require changes to support networking, centralized data storage, distributed access,

better storage capacity, and so forth. In other words, scaling it up would be too expensive

and probably would require a complete rewrite.

Finally, consider an alternative beginning. What if you took the time to create the

first system using a distributed architecture based on REST? With each sub-system being

a different API and having them all talk to each other.

Then you would’ve been able to scale the whole thing much easier; working

independently on each sub-system there would be no need for full rewrites and the

system could potentially keep growing to meet new needs.

CHAPTER 2 API DESIGN BEST PRACTICES

70

Summary

This chapter covered what the developer community considers a “good API,” which

means the following:

• Remembering the Developer eXperience (DX).

• Being able to grow and improve without breaking existing clients

• Having up-to-date documentation

• Providing correct error handling

• Providing multiple SDK and libraries

• inking about security

• Being able to scale, both up and down, as needed

In the next chapter, you’ll learn why Node.js is a perfect match for implementing

everything you’ve learned in this chapter.

CHAPTER 2 API DESIGN BEST PRACTICES

71

F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1_3

CHAPTER 3

Node.js andREST

There are currently too many technologies out there—be it programming languages,

platforms, or frameworks. Why is it, then, that Node.js—a project that’s hasn’t even

reached version 1.0 at the time of this writing—is so popular these days?

Advances in hardware make it possible for developers to focus less on hyper-

optimizing their code to gain speed, allowing them to focus more on speed of

development; thus, a new set of tools has surfaced.

These tools make it easier for novice developers to develop new projects, while at the

same time provide advanced developers with access to the same type of power they got

with the old tools. These tools are the new programming languages and frameworks of

today (Ruby on Rails, Laravel, Symfony, Express.js, Node.js, Django, and much more).

In this chapter, I’ll go over one of the newest of these: Node.js. It was created in 2009

by Ryan Dahl and sponsored by Joyent, the company for which Dahl worked. At its core,

Node.js

1

utilizes the Google V8

2

engine to execute JavaScript code on the server side.

I’ll cover its main features to help you understand why it is such a great tool for API

development.

The following are some of the aspects of Node.js covered in this chapter:

• Async programming: This is a great feature of Node.js. I’ll discuss

how you can leverage it to gain better results than if using other

technologies.

• Async I/O: Although related to async programming, this deserves a

separate mention because in input/output-heavy applications, this

particular feature presents the winning card for choosing Node.js

over other technologies.

1

See http://en.wikipedia.org/wiki/Node.js.

2

See http://en.wikipedia.org/wiki/V8_(JavaScript_engine).

72

• Simplicity: Node.js makes getting started and writing your rst web

server very easy. You’ll see some examples.

• Amazing integration with JSON-based services (like other APIs,

MongoDB, etc.).

• e community and the Node package manager (npm): I’ll go over

the benets of having a huge community of developers using the

technology and how npm has helped.

• Who’s using it?: Finally, I’ll quickly go over some of the big companies

using Node.js in their production platforms.

Asynchronous Programming

Asynchronous (or async) programming is perhaps at the same time one of the best and

most confusing features of Node.js.

Asynchronous programming means that for every asynchronous function that

you execute, you can’t expect it to return the results before moving forward with the

program’s flow. Instead, you’ll need to provide a callback block/function that will be

executed once the asynchronous code finishes.

Figure3-1 shows a regular, non-asynchronous flow.

CHAPTER 3 NODE.JS ANDREST

73

Figure3-1 represents a set of instructions that run in a synchronous manner. To

execute Instruction #4, you need to wait as long as the “long time running instruction”

takes and then wait for Instruction #3 to finish. But what if Instruction #4 and Instruction

#3 weren’t really related? What if you didn’t really mind in which order Instruction #3

and Instruction #4 executed in relationship to each other?

Figure 3-1. A synchronous execution flow

CHAPTER 3 NODE.JS ANDREST

74

Then you could make the “long time running instruction” executed in an

asynchronous manner and provide Instruction #3 as a callback to that, allowing you to

execute Instruction #4 much sooner. Figure3-2 shows how that would look.

Instead of waiting for it to finish, Instruction #4 is executed right after Instruction #2

starts the asynchronous “long time running instruction.”

This is a very simple example of the potential benefits of asynchronous

programming. Sadly, like with most in this digital world, nothing comes without a price,

and the added benefits also come with a nasty trade-off: debugging asynchronous code

can be a real head-breaker.

Developers are trained to think of their code in the sequential way they write it, so

debugging a code that is not sequential can be difficult to newcomers.

For instance, Listings 3-1 and 3-2 show the same piece of code written in a

synchronous and an asynchronous manner, respectively.

Figure 3-2. An asynchronous execution flow

CHAPTER 3 NODE.JS ANDREST

75

Listing 3-1. Synchronous Version of a Simple Read File Operation

console.log("About to read the file... ")

let content = fs.readFileSync("/path/to/file")

console.log("File content: ", content)

Listing 3-2. Asynchronous Version of a Simple File Read Operation with a

Common Mistake

console.log("About to read the file...")

let content = ""

fs.readFile("/path/to/file", function(err, data) {

content = data

})

console.log("File content: ", content)

If you haven’t guessed it yet, Listing 3-2 will print the following:

File content:

and the reason for that is directly related to the diagram shown in Figure3-3. Let’s use it

to see what’s going on with the buggy asynchronous version.

Figure 3-3. The error from Listing 3-2

CHAPTER 3 NODE.JS ANDREST

76

It’s pretty clear why the content of the file is not being written: the callback is

being executed after the last console.log line. This is a very common mistake by new

developers, not only with Node.js, but more specifically with AJAX calls on the front end.

They set up their code in a way to use the content returned by the asynchronous call

before it actually ends.

To finish the example, Listing 3-3 shows how the code needs to be written to

properly work.

Listing 3-3. Correct Version of the Asynchronous File Read Operation

console.log("About to read the file...")

let content = ""

fs.readFile("/path/to/file", function(err, data) {

content = data

console.log("File content: ", content)

})

Simple. You just moved the last console.log line into the callback function, so you’re

sure that the content variable is set correctly.

Async Advanced

Asynchronous programming is not just about making sure that you set up the callback

function correctly, it also allows for some interesting flow control patterns that can be

used to improve the efficiency of the app.

Let’s look at two distinct and very useful control flow patterns for asynchronous

programming: parallel flow and serial flow.

Parallel Flow

The idea behind parallel flow is that the program can run a set of nonrelated tasks in

parallel but only call the callback function provided (to gather their collective outputs)

after all tasks have finished executing.

CHAPTER 3 NODE.JS ANDREST

77

Basically, Listing 3-4 shows what you want.

Listing 3-4. Signature of the Parallel Function

//functionX symbols are references to individual functions

parallel([function1, function2, function3, function4], data => {

///do something with the combined output once they all finished

})

To know when each of the functions passed in the array have finished execution,

they’ll have to execute a callback function with the results of their operation. The

callback will be the only attribute they receive. Listing 3-5 shows the parallel function.

Listing 3-5. Implementation of the Parallel Function

function parallel(funcs, callback) {

var results = [],

callsToCallback = 0

funcs.forEach( fn => { // iterate over all functions

setTimeout(fn(done), 200) // and call them with a 200 ms delay

})

function done(data) { // the functions will call this one when they

finish and they’ll pass the results here

results.push(data)

if(++callsToCallback == funcs.length) {

callback(results)

}

The implementation in Listing 3-5 is very simple, but it fulfills its task: it runs a set

of functions in a parallel way (you’ll see that since Node.js runs in a single thread, true

parallelism is not possible, so this is as close as you can get).

This type of control flow is particularly useful when dealing with calls to external

services.

CHAPTER 3 NODE.JS ANDREST

78

Let’s look at a practical example. Assume your API needs to do several operations

that, although aren’t related to each other, need to happen before the user can see the

results. For instance, load the list of books from the database, query an external service

to get news about new books out this week, and log the request into a file. If you were to

execute all of those tasks in a series (see Listing 3-6), waiting for one to finish before the

next one can be run, then the user would most probably suffer a delay on the response

because the total time needed for the execution is the sum of all individual times.

But if instead you can execute all of them in parallel (see Listing 3-7), then the total

time is actually equal to the time it takes the slowest task to execute.

3

Let’s look at both cases in Listings 3-6 and 3-7.

Listing 3-6. Example of a Serial Flow (takes longer)

//request handling code...

//assume "db" is already initialized and provides an interface to the data base

db.query("books", {limit:1000, page: 1}, books => {

services.bookNews.getThisWeeksNews(news => {

services.logging.logRequest(request, () => { //nothing returned, but

you need to call it so you know the logging finished

response.render({listOfBooks: books, bookNews: news})

})

Listing 3-7. Example of a Parallel Execution Flow

//request handling code...

parallel([

callback => { db.query("books", {limit: 1000, page: 1}, callback) },

callback => { services.bookNews.getThisWeeksNews(callback) },

callback => { services.logRequest(request, callback) }

], data => {

var books = findData("books", data)

3

This is a rough approximation, since the time added by the parallel function needs to be taken

into account for an exact number.

CHAPTER 3 NODE.JS ANDREST

79

var news = findData("news", data)

response.render({listOfBooks: books, bookNews: news})

})

Listings 3-6 and 3-7 show how each approach looks. The findData function simply

looks into the data array and, based on the structure of the items, returns the desired

one (first parameter). In the implementation of parallel a function such as findData is

needed because you can’t be sure in which order the functions finished and then sent

back their results.

Aside from the clear speed boost that the code gets, it’s also easier to read and easier

to add new tasks to the parallel flow—just add a new item to the array.

Serial Flow

The serial flow provides the means to easily specify a list of functions that need to be

executed in a particular order. This solution doesn’t provide a speed boost like parallel

flow does, but it does provide the ability to write such code and keep it clean, staying

away from what is normally known as spaghetti code.

Listing 3-8 shows what you should try to accomplish.

Listing 3-8. Signature of the Serial Function

serial([

function1, function2, function3

], data => {

//do something with the combined results

})

Listing 3-9 shows what you shouldn’t do.

Listing 3-9. Example of a Common Case of Nested Callbacks

function1(data1 => {

function2(data2 => {

function3(data3 => {

//do something with all the output

}

CHAPTER 3 NODE.JS ANDREST

80

You can see how the code in Listing 3-9 could get out of hand if the number of

functions kept growing. So the serial approach helps keep the code organized and

readable.

Let’s look at a possible implementation of the serial function in Listing 3-10.

Listing 3-10. Implementation of the Serial Function

function serial(functions, done) {

let fn = functions.shift() //get the first function off the list

let results = []

fn(next)

function next(result) {

results.push(result) //save the results to be passed into the final

callback once you don’t have any more functions to execute.

let nextFn = functions.shift()

if (nextFn) nextFn(next)

else done(results)

}

There are more variations to these functions, like using an error parameter to handle

errors automatically or limiting the number of simultaneous functions in the parallel flow.

All in all, asynchronous programming brings a lot of benefits to implementing APIs.

Parallel workflow comes in very handy when dealing with external services, which

normally any API would deal with—for instance, database access, other APIs, disk I/O,

and so forth. And at the same time, the serial workflow is useful when implementing

things like Express.js middleware.

4

For a fully functional and tested library that thrives on asynchronous programming,

please check out async.js.

5

4

See http://expressjs.com/guide/using-middleware.html.

5

See https://github.com/caolan/async.

CHAPTER 3 NODE.JS ANDREST

81

Asynchronous I/O

A specific case of asynchronous programming relates to a very interesting feature

provided by Node.js: asynchronous I/O.

This feature is highly relevant to the internal architecture of Node.js. As I’ve said,

Node.js doesn’t provide multi-threading; it actually works with a single thread that runs

an event loop.

Essentially, the Event Loop works on phases; for every tick of the loop, it goes

through a new phase. For every phase, it keeps a FIFO queue of callbacks, and it executes

as many callbacks in that phase as it can (there is a limit to how many callbacks can be

called on every tick).

There is a common misconception that the event loops handles all asynchronous

functions with threads from Libuv (the library V8 uses to handle asynchronism). But

it’s not exactly true; these threads are only used in special cases when there is no

other way, because modern OS and other systems, such as Databases, already provide

asynchronous interfaces, so the engine will try to use them, and if there is no async

alternative, it’ll resort to the thread pool.

The aforementioned phases are:

1. Timers: Here is where setTimeout and setInterval are evaluated.

2. Callbacks: Here is where system-specic callbacks are executed.

3. Poll: is is where I/O-related callbacks get executed, as long

as there are any. Once all callbacks have been executed (or the

system’s limit is reached), if there is nothing else to execute, then

the engine will wait for new callbacks to be registered in this phase

to execute them.

4. Check: Here is where setImmediate is evaluated.

5. Close events: Here is where the callbacks registered for the ‘close’

events are executed.

If you wanted to, there is a very interesting way to look into this and test it on your

own. Simply by using the following code, you’ll see how the execution is done internally:

CHAPTER 3 NODE.JS ANDREST

82

Listing 3-11. Example showing the different phases for the event loop

const request = require("request"),

fibonacci = require("fibonacci"),

fs = require("fs");

process.nextTick(() => {

process.stdout.write("NT #1\n");

});

fs.readFile("./index.js", (err, data) => {

process.stdout.write("1: I/O Polling...\n");

});

request.get("http://google.com", (err, res, body) => {

process.stdout.write("2: System polling...\n");

})

setImmediate(() => {

process.stdout.write("3: Set Immediate phase...\n");

});

setTimeout(() => {

process.stdout.write("4: Timers...\n");

}, 0);

process.stdout.write("5: Fibonacci(20): " + fibonacci.iterate(20).number +

" -Callback\n");

process.nextTick(() => {

process.stdout.write("NT #2\n");

})

The result from executing the code from Listing 3-11 is the following (note that this is

in my computer, with Node version 8.1.3; results might vary on your side, but they should

be similar nonetheless):

1. 5: Fibonacci(20): 6765 callback

2. NT #1

3. NT #2

CHAPTER 3 NODE.JS ANDREST

83

4. 4: Timers…

5. 3: Set Immediate phase…

6. 1: I/O Polling…

7. 2: System polling…

From these results, we can extrapolate the following behavior:

1. The first thing to get executed (and resolved) is the current thread,

which means the line of the fibonacci call. The rest of the lines

were executed, but they have not yet resolved, because they’re all

different forms of asynchronous behavior.

2. After the current phase is over, the event loop tries to move to the

next one, but rst it needs to call the nextTick method, which is

executed on a separate queue. is means that no matter what the

current phase is, it’ll resolve all callbacks you’ve dened and then

move to the next phase.

3. By this time, the Poll phase has probably run, and it has veried

that no callback has been registered for it yet (because the le is

still being read and the HTTP Request is still being made), so it

continues to the timers and check phases.

4. In this case, depending on the performance of your system, either

one of them can run. e point here is that since we’ve setup the

timeout for setTimeout to 0, the execution of that callback and the

one for setImmediate is non-deterministic. In other words, you

won’t be able to predict their order of execution.

6

5. Finally, after the timers have run, the only thing missing is to wait

on the Poll phase until the I/O operations end, and given the

nature of them, reading the file will end first, leaving the HTTP

request to be resolved in the last place.

6

See Node.js’ official documentation about this: https://nodejs.org/en/docs/guides/

event-loop-timers-and-nexttick/#process-nexttick-vs-setimmediate

CHAPTER 3 NODE.JS ANDREST

84

Figure3-4 attempts to present a graphical representation of the preceding events,

starting from what would be step 3.

You can read more on the how the event loop works from the official documentation,

but this should give you a basic idea of how it should work. You can tweak and change

the code sample from Listing 3-11 to see how the results change until you’re sure there is

no witchcraft involved. (I know it took me several attempts to get there.)

Figure 3-4. Graphical representation of how the event loop would work for the

code of listing 3-11

CHAPTER 3 NODE.JS ANDREST

85

Async I/O vs. Sync I/O

Finally, for the sake of proving that everything I’ve stated so far is true and that Node.js

works best using async I/O, I’ve done some very simple benchmarking. I’ve created a

simple API with two endpoints:

• /async: This reads a 1.6MB file asynchronously before returning a

simple JSON response.

• /sync: This reads a 1.6MB file synchronously before returning a

simple JSON response.

Both endpoints do exactly the same, only in a different manner (see Listing 3-11).

The idea is to prove that even in such simple code, the event loop can handle multiple

requests better when the underlying code makes use of the asynchronous I/O provided

by the platform.

Listing 3-12 is the code of both endpoints; the API was written using Vatican.js.

7

Listing 3-12. Example of Two Endpoints Coded Using the Express.js Framework

//Async handler

const fs = require("fs")

class AsyncHdlr {

constructor() {

}

@endpoint(url: /async method: get)

index(req, res, next) {

let fname = __dirname + "/file.txt";

fs.appendFile(fname, Date.now(), (err, content) => {

res.send({

success: true

})

}

7

See https://www.npmjs.com/package/vatican

CHAPTER 3 NODE.JS ANDREST

86

module.exports = AsyncHdlr;

//Sync handler

const fs = require("fs")

class SyncHdlr {

constructor() {

}

@endpoint(url: /sync method: get)

index(req, res, next) {

let fname = __dirname + "/file.txt";

fs.appendFileSync(fname, Date.now());

res.send({

success: true

});

}

module.exports = SyncHdlr;

The benchmark was done using the Apache Benchmark

8

tool using the following

parameters:

• Number of requests: 10,000

• Concurrent requests: 100

8

See http://httpd.apache.org/docs/2.2/programs/ab.html.

CHAPTER 3 NODE.JS ANDREST

87

The results are shown in Table3-1.

As you can see in Table3-1, for even the simplest of examples, there are 812 more

requests being served by the asynchronous code than in the synchronous code in

the same amount of time. Another interesting item is that each request is almost 8

milliseconds faster on the asynchronous endpoint; this might not be a huge number, but

considering the nonexistent complexity of the code you’re using, it’s quite relevant.

Simplicity

Node.js (more specifically, JavaScript) is not a complicated language. It follows the basic

principles that similar scripting languages follow (like Ruby, Python, and PHP), but

with a twist (like all of them do). Node.js is simple enough for any developer to pick up

and start coding in no time, and yet it’s powerful enough to achieve almost anything

developers can set their minds to.

Although JavaScript is an amazing language, and a focus of this book, like I’ve

said and will keep saying: there are no silver bullets when it comes to programming.

JavaScript has gained a lot of traction over the years, but it has also gained a lot of haters,

and they have their very valid reasons: a nonstandard object-oriented model, weird

usage of the “this“ keyword, a lack of functionality built into the language (it has a lot of

libraries dedicated to implementing basic features that come built-in in other languages),

and the list goes on. In the end, every tool needs to be chosen based on its strengths.

Node.js is a particularly strong option for developing APIs, as you’re about to see.

Node.js adds a certain useful flavor to the language, simplifying a developer’s life

when trying to develop back-end code. It not only adds the required utilities to work with

I/O (which front-end JavaScript doesn’t have for obvious security reasons), but it also

provides stability for all the different flavors of JavaScript that each web browser supports.

Table 3-1. Results from the Benchmark of the Two Endpoints Shown in Listing 3-11

Synchronous Endpoint Asynchronous Endpoint

Requests per second: 3065.00[#/sec.] (mean)

Time per request 32.4626 [ms] (mean)

Time per request: 0.326 [ms] (mean, across all

concurrent requests)

Transfer rate: 652.51 [KBps] received

Requests per second: 3877.82 [#/sec.] (mean)

Time per request: 25.788 [ms] (mean)

Time per request: 0.258 [ms] (mean, across all

concurrent requests)

Transfer rate: 825.55 [KBps] received

CHAPTER 3 NODE.JS ANDREST

88

One example of this is how easy it is to set up a web server with just a few lines of

code. Let’s look at that in Listing 3-13.

Listing 3-13. Simple Example of a Web Server Written in Node.js

const http = require("http")

http.createServer((req, res) => { //create the server

//request handler code here

});

http.listen(3000) //start it up on port 3000

JavaScript also has the advantage of being the standard front-end language for all

commercial web browsers, which means that if you’re a web developer with front-end

experience, you have certainly come across JavaScript.

This makes it simpler for the developer who’s migrating from the front end into the

back end; since the language basics haven’t changed, you only need to learn about the

new things and change into a back-end mindset. At the same time, this helps companies

find Node.js developers faster.

With all that in mind, let's look at some of the main characteristics of JavaScript that

make it such a simple (and yet powerful) option.

Dynamic Typing

Dynamic typing is a basic characteristic present in most common languages nowadays,

but it’s no less powerful because of that. This little feature allows the developer to not

have to think too much when declaring a variable; just give it a name and move on.

Listing 3-14 shows something you can’t do with a statically typed language.

Listing 3-14. Example of Code Taking Advantage Of Dynamic Typing

var a, b, tmp //declare the variables (just give them names)

//initialize them with different types

a = 10

b = "hello world"

//now swap the values

tmp = a

CHAPTER 3 NODE.JS ANDREST

89

a = b // even with automatic casting, a language like C won't be able to

cast "hello world" into an integer value

b = tmp

console.log(a) //prints "hello world"

console.log(b) //prints 10

Object-Oriented Programming Simplified

JavaScript it not an object-oriented language, but it does have support for some of these

features (see Listing 3-14 and Listing 3-16). You’ll have enough access to objects to

conceptualize problems and solutions using them, which is always a very intuitive way

of thinking, but at the same time, you're not dealing with concepts like polymorphism,

interfaces, or others that, despite helping to structure code, have proven to be

dispensable when designing applications.

Listing 3-15. Simplified Object Orientation Example

var myObject = { //JS object notation helps simplify definitions

myAttribute: "some value",

myMethod: function(param1, param2) {

//does something here

}

//And the just...

myObject.myMethod(...)

Whereas with other languages, like Java (a strongly object-oriented language), you

would have to do what’s shown in Listing 3-16.

Listing 3-16. Example of a Class Definition in Java

class myClass {

public string myAttribute;

public myClass() {

}

public void myMethod(int param1, int param2) {

//does something here

}

CHAPTER 3 NODE.JS ANDREST

90

//And then

myClass myObj = new myClass();

myObj.myMethod(...);

Much less verbose, isn’t it?

In Listing 3-17, let’s look at another example of the powerful object orientation that

you have available.

Listing 3-17. Another Example of the Features Provided by Object Orientation in

JavaScript

var aDog = { //behave like a dog

makeNoise: function() {

console.log("woof!");

}

var aCat = { //behave like a cat

makeNoise: function() {

console.log("Meewww!");

}

var myAnimal = { //our main object

makeNoise: function() {

console.log("cri... cri....")

},

speak: function() {

this.makeNoise()

}

myAnimal.speak() //no change, so.. crickets!

myAnimal.speak.apply(aDog) //this will print "woof!"

//switch behavior

myAnimal.speak.apply(aCat) //this will now print "Meewww!"

CHAPTER 3 NODE.JS ANDREST

91

You were able to encapsulate a simple behavior into an object and pass it into

another object to automatically overwrite its default behavior. That’s something that’s

built into the language; you didn’t have to write any specific code to achieve this feature.

The new Class construct fromES6

Tired of being laughed at and pointed at for not having a proper class construct for the

OOP lovers, the good folks at Ecma International decided to create one. Actually, I’m just

guessing, I don’t know why they decided to add it, but they did, so be happy about it or

don’t, your call.

The point is: if you like solving your problems using OOP, now you have the most

basic structure any OOP language provides, right at your fingertips. But don’t get too

excited just yet, they’re not the same kind of classes you’d have in JAVA or any other fully

OOP language. No, they’re just your basic, nothing-fancy type of classes, and let me

explain with the following code sample:

Listing 3-18. Example of Classes in ES6

"use strict";

class AnotherClass {

constructor(p1, p2) {

this._param1 = p1;

this._param2 = p2;

}

class SampleClass extends AnotherClass {

constructor(param1, param2) {

super(param1, param2)

}

set param1(val) {

this._param1 = +val;

}

CHAPTER 3 NODE.JS ANDREST

92

set param2(val) {

this._param2 = +val;

}

get param1() {

return "This is param1: " + this._param1;

}

get sum() {

return this._param1 + this._param2;

}

static description() {

return "This is a static method, like the ones you're used

to using...";

}

let sampleObj = new SampleClass(1,2);

console.log(sampleObj.sum);

sampleObj.param1 = "100";

console.log(sampleObj.sum);

console.log(sampleObj.param1);

console.log(SampleClass.description());

Like I said, nothing controversial nor complicated, the code sample shows the basic

features of the classes that come with ES6, which are:

• Inheritance: Using the extends reserved word, you can quickly tell

which class inherits from another one.

• Reserved word constructor: Yes, you do have a quirk here; instead of

following the old convention of using the class name to identify the

constructor code, you can actually dene it using a function called

constructor.

• Getters and setters: is is one that I actually think is pretty neat.

You get methods that you can dene to add extra code needed when

setting or getting a specic property on your class.

CHAPTER 3 NODE.JS ANDREST

93

• No privacy in your code: ere is no way to dene the visibility of

your methods and properties; everything is public, deal with it.

• Static methods: Finally, we also got static methods, which help to

clean up the code.

Tip Setters are quite useful and easy to set up; just remember to not name them

exactly like the property you’re trying to affect, otherwise you’ll get a recursion

error trying to setting inside the actual setter.

Functional Programming Support

JavaScript is not a functional programming language; but then again, it does have

support for some of its features (see Listings 3-18, 3-19, and 3-20), such as having first-

class citizen functions, allowing you to pass them around like parameters, and returning

closures easily. This feature makes it possible to work with callbacks, which, as you’ve

already seen, is the basis for asynchronous programming.

Let’s look at a quick and simple functional programming example in Listing 3-19

(remember, JavaScript provides only some functional programming goodies, not all of

them). Create an adder function.

Listing 3-19. Simple Example of an Adder Function Defined Using Functional

Programming

function adder(x){

return function(y) {

return x+y

}

var add10 = adder(10) //you create a new function that adds 10 to whatever

you pass to it.

console.log(add10(100)) //will output 110

Let’s look at a more complex example, an implementation of the map function,

which allows you to transform the values of an array by passing the array and the

transformation function. Let’s first look at how you’d use the map function.

CHAPTER 3 NODE.JS ANDREST

94

Listing 3-20. Example of a Map Function Being Used

map([1,2,3,4], x => { return x * 2 }) //will return [2,4,6, 8]

map(["h","e","l","l","o"], String.prototype.toUpperCase)

//will return ["H","E","L","L","O"]

Now let’s look at a possible implementation using the functional approach.

Listing 3-21. Implementation of a Map Function, Like the One Used in Listing 3-19

function reduce(list, fn, init) {

if(list.length == 0) return init

let value = list[0]

init.push(fn.apply(value, [value])) //this will allow us to get

both the functions that receive the value as parameters and the

methods that use it from it's context (like toUpperCase)

return reduce(list.slice(1), fn, init) //iterate over the list

using it's tail (everything but the first element)

}

function map(list, fn) {

return reduce(list, fn, [])

}

Duck Typing

Have you ever heard the phrase “If it looks like a duck, swims like a duck, and quacks like

a duck, it probably is a duck”? Well then, it’s the same for typing in JavaScript. The type of

a variable is determined by its content and properties, not by a fixed value. So the same

variable can change its type during the life cycle of your script. Duck typing is both a very

powerful feature and a dangerous feature at the same time.

Listing 3-22 offers a simple demonstration.

Listing 3-22. Quick Example of Duck Typing in JavaScript

var foo = "bar"

console.log(typeof foo) //will output "string"

foo = 10

console.log(typeof foo) //this will now output "number"

CHAPTER 3 NODE.JS ANDREST

95

Native Support forJSON

This is a tricky one, since JSON actually spawned from JavaScript, but let’s not get into

the whole chicken-and-egg thing here. Having native support for the main transport

language used nowadays is a big plus.

Listing 3-23 is a simple example following the JSON syntax.

Listing 3-23. Example of How JSON Is Natively Supported by JavaScript

var myJSONProfile = {

"first_name": "Fernando",

"last_name": "Doglio",

"current_age": 30,

"married": true,

"phone_numbers": [

{

"home_phone": "59881000293",

"cell_phone": "59823142242"

}

]

}

//And you can interact with that JSON without having to parse it or

anything

console.log(myJSONProfile.first_name, myJSONProfile.last_name)

This particular feature is especially useful in several cases—for instance, when

working with a document-based storage solution (like MongoDB) because the modeling

of data ends up being native in both places (your app and the database). Also, when

developing an API, you’ve already seen that the transport language of choice these days is

JSON, so the ability to format your responses directly with native notation (you could even

just output your entities, for that matter) is a very big plus when it comes to ease of use.

The list could be extended, but those are some pretty powerful features that

JavaScript and Node.js bring to the table without asking too much of the developer. They

are quite easy to understand and use.

CHAPTER 3 NODE.JS ANDREST

96

Note The features mentioned are not unique to JavaScript; other scripting

languages have some of them as well.

npm: TheNode Package Manager

Another point in favor of Node.js is its amazing package manager. As you might know

by now (or are about to find out), development in Node is very module-dependent,

meaning that you’re not going to be developing the entire thing; most likely, you’ll be

reusing someone else’s code in the form of modules.

This is a very important aspect of Node.js, because this approach allows you to

focus on what makes your application unique and lets the generic code be integrated

seamlessly. You don’t have to recode the library for HTTP connectivity, nor your route

handler on every project (in other words, you don’t have to keep reinventing the wheel);

just set the dependencies of your project into the package.json file using the best-suited

module names, and then npm will take care of going through the whole dependency tree

and will install everything needed (think of APT for Ubuntu or Homebrew for Mac).

The amount of active users and modules available (more than 100,000 packages and

more than 600 million downloads a month) assures you that you’ll find what you need;

and in the rare occasions when you don’t, you can contribute by uploading that specific

module to the registry and help the next developer that comes looking for it.

This amount of modules can also be a bad thing since such a large number means

that there will be several modules that try to do the same thing. (For instance, e-mail-

validation, sane-e-mail-validation, mailcover, and mailgun-e-mail-validation all try to

do the same thing—validate an e-mail address using different techniques; depending

on your needs, you have to pick one.) You have to browse through them to find the best

suited candidate.

This is all possible thanks to the amazing community of developers that have formed

since Node.js hit the shelves in 2009.

To start using npm, just visit their site at www.npmjs.org. There you’ll see a list of

recently updated packages to get you started (as seen in Figure3-5) and some of the

most popular ones as well.

CHAPTER 3 NODE.JS ANDREST

97

If want to install it directly, just write the following line into your Linux console:

$ curl https://www.npmjs.org/install.sh | sh

You need to have Node.js version 0.8+ installed to use it properly. Once that is done,

you can begin installing modules by simply typing:

$ npm install [MODULE_NAME]

This command downloads the specified module into a local folder called

node_modules; so try to run it from within your project’s folder.

You can also use npm to develop your own modules and publish them into the site

by using the following:

$ npm publish #run this command from within your project's folder

The preceding command takes attributes from the package.json file, packages the

module, and uploads everything into npm’s registry. After that, you can go into the site

and check for your package; it’ll be listed there.

Figure 3-5. The npm site

CHAPTER 3 NODE.JS ANDREST

98

Note Aside from checking out www.npmjs.org, you can also check the Google

Groups nodejs

9

and nodejs-dev

10

for a direct connection to people in the Node.js

community.

Who’s Using Node.js?

This entire book is meant to validate and provide examples of how good Node.js is

when it comes to developing RESTful systems, but also how valid the idea of having

Node.js-powered systems running in production (this is the hardest obstacle to

overcome, especially when trying to convince your boss of switching stacks into a

Node.js-based one).

But what better validation, then, than to look at some of the most important users of

Node.js in production?

• PayPal: Uses Node.js to power its web application

• eBay: Uses Node.js mainly due to the benets that asynchronous I/O brings

• LinkedIn: e entire back-end mobile stack is done in Node.js. e two

reasons for using it are scale and performance gained over the previous

stack.

• Netix: Uses Node.js on several services; often writes about experiences

using Node.js on its tech blog at http://techblog.netﬂix.com

• Yahoo!: Uses Node.js on several products, such as Flickr, My Yahoo!, and

home page)

This list could go on and include a very large list of other companies, some more

well-known than others, but the point remains: Node.js is used for production services

all over the Internet, and it handles all kinds of traffic.

9

See https://groups.google.com/forum/#!forum/nodejs.

10

See https://groups.google.com/forum/#!forum/nodejs-dev.

CHAPTER 3 NODE.JS ANDREST

99

Summary

This chapter covered the advantages of Node.js for the common developer, especially

how its features improve the performance of I/O–heavy systems such as APIs.

In the next chapter, you’ll get more hands-on and learn about the basic architecture

and tools you’ll use to develop the API in the final chapter.

CHAPTER 3 NODE.JS ANDREST

101

F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1_4

CHAPTER 4

Architecting aREST API

It is extremely important to understand a REST-based architecture, meaning how the

system will look if you’re basing all of your services in the REST style. But it is equally

important to know what the internal architecture of those REST services will look like

before you start working.

In Node.js there are several modules out there, with thousands of daily downloads

that can help you create an API without having to worry too much about the internal

aspects of it. And that might be a good idea if you’re in a hurry to get the product out,

but since you’re here to learn, I’ll go over all the components that make up a standard,

general-purpose REST API.

The modules are mentioned, but I won’t go into details on how they’re used or

anything; that will come in the next chapter—so keep reading!

For the purpose of this book, I’ll take the traditional approach when it comes to

architecting the API, and you’ll use an MVC pattern (model–view–controller); although

you might be familiar with other options, it is one of the most common ones and it

normally fits well as a web use case.

The basic internal architecture of a RESTful API contains the following items:

• A request handler: This is the focal point that receives every request

and processes it before doing anything else.

• A middleware/pre-process chain: ese guys help shape the request

and provide some help for authentication control.

• A routes handler: After the request handler is done, and the request

itself has been checked and enriched with everything you need, this

component gures out who needs to take care of the request.

• e controller: is guy is responsible for all requests done related to

one specic resource.

102

• e Model: Also known as the resource in our case. You’ll focus most

of the logic related to the resource in here.

• e representation layer: is layer takes care of creating the

representation that is visible to the client app.

• e response handler: Last but certainly not least, the response

handler takes care of sending the representation of the response back

to the client.

Note As I’ve stated several times before, this book focuses on HTTP-based

REST, which means that any request mentioned in this chapter is an HTTP request,

unless otherwise stated.

The Request Handler, thePre-Process Chain,

andtheRoutes Handler

The request handler, the pre-process chain, and the routes handler are the first three

components in any request to your system, so they’re key to having a responsive and

fast API.Luckily, you’re using Node.js, and as you saw in Chapter 3, Node.js is great at

handling many concurrent requests because of its event loop and async I/O.

That being said, let’s list the attributes our request handler needs to have for our

RESTful system to work as expected:

• It has to gather all the HTTP headers and the body of the request,

parse them, and provide a request object with that information.

• It needs to be able to communicate with both the pre-processing

chain module and the routes handler to gure out which controller

needs to be executed.

• It needs to create a response object capable of nishing and

(optionally) writing a response back to the client.

CHAPTER 4 ARCHITECTING AREST API

103

Figure4-1 shows the steps that are part of the initial contact between client and

server:

1. The client application issues a request for a particular resource.

2. e request handler gathers all information. It creates a request

object and passes it along to the pre-processing chain.

3. Once nished, the pre-processing chain returns the request

object—with whatever changes made to it—to the request

handler.

4. Finally, the RH sends the request and response objects to the

routes handler so that the process can continue.

Figure 4-1. Example of how the request handler and its interactions with other

components look

There is one problem in Figure4-1 that jumps right out at you (or it should): if the

pre-processing chain takes too long, the request handler must wait for it to finish before

handing over the request to the routes handler, and any other incoming request is forced

to wait as well.

This can be especially harmful to the performance of the API if the pre-processing

chain is doing some heavy-duty tasks, like loading user-related data or querying external

services.

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Thanks to the fact that you’re using Node.js as the basis for everything here, you can

easily change the pre-processing chain to be an asynchronous operation. By doing that,

the request handler is able to receive new requests while still waiting for the processing

chain from the previous request. Figure4-2 shows how the diagram would change.

As you can see in Figure4-2, the change is minimal, at least at the architectural

level. The request handler sets up a callback to the routes handler, and that callback

is executed once the pre-processing chain is finished. And right after setting up the

callback, the request handler is free again for the next request. This clearly provides more

freedom to this component, allowing the entire system to process more requests per

second.

Note This change will not actually speed up the pre-processing chain time of

execution. Neither will it speed up the time it takes a single request to be finished,

but it will allow the API to handle more requests per second, which in practice

means avoiding an obvious bottleneck.

Figure 4-2. Changes to the architecture show how to improve it by using a callback

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As for the pre-processing chain, you’ll use it for generic operations, things that are

required in most of the routes you’ll handle. That way you can extract that code from the

handlers and centralize it into small units of code (functions) that are called in sequence

for every request.

Most of the modules you’ll see in Chapter 5 have one version of the pre- processing

chain. For instance, Express.js calls the functions that can be executed in the chain

“middleware.” Vatican.js calls them “pre-processors” to differentiate them from the

post-processors that the module also provides.

Tip The main rule to remember when adding a new function into this chain is

that as a good practice, the function should take care of one task, and one task

only. (This is generally a good practice to follow on every aspect of software

development. Some call it the Unix Philosophy, others call it KISS; call it whatever

you want, it’s a good idea to keep in mind.) That way, it becomes mind-blowingly

easy to enable and disable them when testing, even to alter their order. On the

other hand, if you start adding functions that take care of more than one thing,

like authenticating the user and loading his/her preferences, you’ll have to edit the

function’s code to disable one of those services.

Since you’ll want the entire pre-processing to be done asynchronously to release the

request handler from waiting for the chain to be done, the chain will use asynchronous

serial flow. This way you can be sure of the order of execution; but at the same time,

you’re free to have these functions perform actions that take longer than normal, like

asynchronous calls to external services, I/O operations, and the like.

Let’s take a final look at the last diagram. So far it looks great: you’re able to handle

requests asynchronously and you can do some interesting things to the request by

pre-processing it before giving it to the routes handler. But there is one catch: the

pre- processing chain is the same for all routes.

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That might not be a problem if the API is small enough, but just to be on the safe

side, and to provide a fully scalable architecture, let’s take a look at another change that

can be done over the current version to provide the freedom you require (see Figure4-3).

This chain (as shown in Figure4-3) is bigger than the previous one, but it does solve

the scaling problem. The process has now changed into the following steps:

1. The client application issues a request for a particular resource.

2. e request handler gathers all information. It creates a request

object and passes it along to the request handler to return the

right controller. is action is simple enough to do synchronously.

Ideally, it should be done in constant time (O(1)).

3. Once it has the controller, it registers an asynchronous operation with

the correct pre-processing chain. is time around, the developer

is able to set up as many chains as needed and associates them to

one specic route. e request handler also sets up the controller’s

method to be executed as the callback to the chain’s process.

4. Finally, the callback is triggered, and the request and response

objects are passed into the controller’s method to continue the

execution.

Figure 4-3. Change on the architecture to provide room for multiple

pre- processing chains

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Note Step 2 mentions that the controller lookup based on the request should be

done in constant time. This is not a hard requirement but should be the desirable

result; otherwise, when handling many concurrent requests, this step might

become a bottleneck that can affect subsequent requests.

MVC: a.k.a. Model–View–Controller

The model–view–controller (MVC) architectural pattern

1

is probably the most well-

known pattern out there. Forget about the Gang of Four’s design patterns,

2

forget about

everything you learned about software design and architectural patterns; if you’re

comfortable with MVC, then you have nothing to worry about.

Actually, that’s not true; well, most of it isn’t anyway. MVC is currently among the

most well-known and used design patterns on web projects (that much is true). That

being said, you should not forget about the others; in fact, I highly recommend you

actually get familiar with the most common design patterns (aside from MVC of course),

like Singleton, Factory, Builder, Adapter, Composite, Decorator, and so forth. Just look

them up, and read and study some examples; it’s always handy to have them as part of

your tool box.

Going back to MVC, even though it has become really popular in the last few years,

especially since 2007 (coincidently the year when version 2 of Ruby on Rails, a popular

web framework that had MVC as part of its core architecture, was released), this bad boy is

not new. In fact, it was originally described by Krasner and Pope in 1988 at SmallTalk- 80

3

as a design pattern for creating user interfaces.

The reason why it is such a popular pattern on web projects is because it fits perfectly

into the multilayer architecture that the web provides. Think about it: due to the client–

server architecture, you already have two layers there, and if you organized code to split

some responsibilities between orchestration and business logic, you gain one more layer

on the server side, which could translate into the scenario shown in Table4-1.

1

See http://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller.

2

See http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/

dp/0201633612/.

3

See http://dl.acm.org/citation.cfm?id=50757.50759.

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Note Prior to Table4-1, I mentioned that the client–server architecture provided

the first two layers for MVC, meaning that the client would act as the presentation

layer. This is not entirely true, as you see later on, but it does serve as a conceptual

layer, meaning that you’ll need a way for the application to present the information

to the user (client).

Table 4-1. List of Layers

Layer Description

Business logic You can encapsulate the business logic of the system into different

components, which you can call models. They represent the different

resources that the system handles.

Orchestration The models know how to do their job, but not when or what kind of data

to use. The controllers take care of this.

Representation layer Handles creating the visual representation of the information. In a normal

web application, this is the HTML page. In a RESTful API, this layer takes

care of the different representations each resource has.

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Let’s look at the diagram in Figure4-4, which represents Table4-1.

Figure4-4 shows the decoupling of the three components: the controller, the model

(which in this case you can also call the resource), and the view. This decoupling allows

for a clear definition of each component’s responsibilities, which in turn helps keep the

code clean and easy to understand.

Figure 4-4. The interaction between the three layers

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Although this is great, the pattern has changed a bit ever since it was adopted by

some web development frameworks, like Ruby on Rails; it now looks more like what’s

shown in Figure4-5.

The current iteration of the pattern removed the relationship between the model

and the view, and instead gave the controller that responsibility. The controller now also

orchestrates the view.

This final version is the one you’ll add into our current growing architecture. Let’s

take a look at how it will look (see Figure4-6).

Figure 4-5. MVC applied to the web

Figure 4-6. The architecture with the added MVC pattern

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Steps 5 and 6 have been added to our architecture. When the right method on

the controller is triggered (in step 4), it handles interacting with the model, gathers

the required data, and then sends it over to the view to render it back to the client

application.

This architecture works great, but there is still one improvement that can be done.

With our RESTful API, the representations are strictly related to the resources data

structure, and you can generalize the view into a view layer, which will take care of

transforming the resources into whatever format you require. This change simplifies

the development since you centralize the entire view-related code into one single

component (the view layer).

The diagram in Figure4-7 might not have changed a lot, but the change in the view

box into a view layer represents the generalization of that code, which initially implied

that there would be one specific view code for every resource.

Figure 4-7. View layer added to the architecture

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Alternatives toMVC

MVC is a great architecture. Nearly every developer is using it or has used it for a web

project. Of course, not everyone loves it, because it has suffered the same fate other

popular things in the development community have suffered (Ruby on Rails, anyone?).

If it becomes popular on the Internet, everyone is using it for everything—until they

realize that not every project looks like an MVC nail, so you have to start looking at other

shapes of hammers (other alternatives architectures).

But luckily, there are alternatives; there are similar architectural patterns that may

better suit your needs, depending on the particular aspects of your project. Some of

them are direct derivatives of MVC, and others try to approach the same problem from a

slightly different angle (I say “slightly” because, as you’re about to see, there are things in

common).

Hierarchical MVC

4

is a more complex version of MVC in the sense that you can nest one

MVC component inside another one. This gives developers the ability to have things like

an MVC group for a page, another MVC group for the navigation inside the page, and a

final MVC component for the contents of the page.

This approach is especially helpful when developing reusable widgets that can be

plugged into components, since each MVC group is self-contained. It is useful in cases

when the data to be displayed come from different related sources. In these cases, having

an HMVC structure helps keep the separation of concerns intact and avoids coupling

between components that shouldn’t be.

Let’s look at a very basic example. Think of a user reading a blog post and the related

comments underneath it. There are two ways to go about it: with MVC or with HMVC.

With MVC, the request is done to the BlogPosts controller, since that is the main

resource being requested; afterward, that controller loads the proper blog post model,

and using that model’s ID, it loads the related comments models. Right there, there is an

unwanted coupling between the BlogPosts controller and the comments model. You can

see this in the diagram in Figure4-8.

4

See http://en.wikipedia.org/wiki/Hierarchical_model%E2%80%93view%E2%80%93controller.

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Figure 4-8. The problem that HMVC tries to solve

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114

Figure4-8 shows the coupling that you need to get rid of; it is clearly something that

can be improved from an architectural point of view. So let’s look at what this would look

like using HMVC (see Figure4-9).

The architecture certainly looks more complex and there are more steps, but it is

also cleaner and easier to extend. Now in step 3, you’re sending a request to an entirely

new MVC component, one in charge of dealing with comments. That component will

in turn interact with the corresponding model and with the generic view layer to return

the representation of the comments. The representation is received by the BlogPost

Figure 4-9. The same diagram with the HMVC pattern applied

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115

controller, which attaches it to the data obtained from the BlogPost model and sends

everything back into the view layer.

If you want to create a new section in the blog showing specific blog posts and their

comments, you could easily reuse the comments component.

All in all, this pattern could be considered a specialization of common MVC, and it

could come in handy when designing complex systems.

Model–View–ViewModel

The Model–View–ViewModel pattern

5

was created by Microsoft in 2005 as a way to

facilitate UI development using WPF and Silverlight; it allows UI developers to write

code using a markup language (called XAML) focusing on the User Experience (UX), and

accessing the dynamic functionalities using bindings to the code. This approach allows

developers and UX developers to work independently without affecting each other’s work.

Just like with MVC, the Model in this architecture concentrates the business logic,

while the ViewModel acts as a mediator between the Model and the View, exposing the

data from the Model. It also contains most of the view logic, allowing the ViewLayer to

only focus on displaying information, leaving all dynamic behavior to the ViewModel

(see Figure 4-10 for more details).

These days, the pattern has been adopted by others outside Microsoft, like the

ZK framework in Java and KnockoutJS, AngularJS, Vue.js, and other frameworks in

JavaScript (since MVVM is a pattern specializing in UI development, it makes sense that

UI frameworks written in JavaScript are big adopters of this pattern).

5

See http://en.wikipedia.org/wiki/Model_View_ViewModel.

Figure 4-10. An MVVC architecture

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Model–View–Adapter

The model–view–adapter

6

(MVA) pattern is very similar to MVC, but with a couple

of differences. Mainly, in MVC the main business logic is concentrated inside each

model, which also contains the main data structure, with the controller in charge of

orchestrating the model and the view.

In MVA, the model is just the data that you’re working with, and the business logic is

concentrated in the adapter, which is in charge of interacting both with the view and the

model. So basically, it consists of slimmer models and fatter controllers. But joking aside,

this allows for a total decoupling of the view and the model, giving all responsibilities to

the adapter.

This approach works great when switching adapters to achieve different behaviors

on the same view and model.

The architecture for this pattern is shown in Figure4-11.

Response Handler

The final component to our API architecture is the response handler; it is in charge of

grabbing the resource representation from the view layer and sending it back to the

client. The response format (which is not the same as the representation’s format) must

be the same as the request’s format; in this case, it’ll be an HTTP 1.1 message.

The HTTP response has two parts: the header, which contains several fields

specifying properties about the message, and the body. The content of the message’s

body is the actual representation of the resource. The header is the section that interests

us the most right now; it contains fields like content-type, content-length, and so on.

6

See http://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93adapter.

Figure 4-11. The MVA pattern shown as a diagram

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Some of those fields are mandatory and some of them are required if you intend to

follow the REST style fully (which you do).

• Cacheable: From the constraints imposed by REST defined in

Chapter 1. Every request must be explicitly or implicitly set as

cacheable when applicable. This translates into the use of the HTTP

header cache-control.

• Content-type: e content type of the response’s body is important

for the client application to understand how to parse the data. If

your resources only have one possible representation, the content

type might be an optional header since you could notify the client

app developer about the format through your documentation. But if

you were to change it in the future, or add a new one, then it might

cause some serious damage to your clients. So consider this header

mandatory.

• Status: e status code is not mandatory but extremely important, as

I’ve mentioned in previous chapters. It provides the client application

a quick indicator of the result of the request.

• Date: is eld should contain the date and time when the message

was sent. It should be in HTTP-date format

7

(e.g., Fri, 24 Dec 2014

23:34:45 GMT).

• Content-length: This field should contain the number of bytes

(length) of the body of the message transferred.

Let’s look at an example of an HTTP response with the JSON representation of a

resource:

HTTP/1.0 200 OK

Date: Fri, 31 Dec 1999 23:59:59 GMT

Content-Type: application/json

Cache-control: private, max-age=0, no-cache

Content-Length: 1354

{

7

See http://tools.ietf.org/html/rfc7231#section-7.1.1.1.

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"name": "J.K.Rolling",

"id": "ab12351bac",

"books": [

{

"title": "Harry Potter and the Philosopher's Stone",

"isbn": "9788478888566"

},

{

"title": "Harry Potter and the Prisoner of Azkaban",

"isbn": "9788422685227"

}

]

}

There is one more improvement that could be made on the response handler if you

want to get some extra juice. This is entirely extra, and most of the Node.js frameworks

out there don’t have it (with the exception of Vatican.js).

The idea is to have a post-processing chain of functions that receives the response

content returned by the view layer, and transforms it, or enriches it if you will, with

further data. It would act as the first version of the pre-processing chain: one common

chain for the entire process.

With this idea, you can abstract further code from the controllers just by moving it

into the post-processing stage. Code-like schema validation (which I’ll discuss later in

the book) or response header setup can be centralized here, and with the added extra of

a simple mechanism for switching your code around or disabling steps in the chain.

Let’s take a look at the final architecture of our API (see Figure4-12).

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119

Figure 4-12. The final architecture with the response handler and the added

post- processing chain

Summary

This chapter covered the basics for a complete and functional RESTful API architecture.

It even covered some extras that aren’t required but are certainly nice to have, such as

pre-and post-processing. You also looked at the main architecture behind our design

(MVC) and some alternatives to it, in case your requirements aren’t a perfect match for

the MVC model.

In the next chapter, I’ll start talking about the modules you’ll use to write the

implementation of this architecture.

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F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1_5

CHAPTER 5

Working withModules

As I discussed in Chapter 3, Node.js has a huge community of developers behind it; they

are willing to put hours and effort into providing the rest of the people in that community

with high-quality modules.

In this chapter, I’ll talk about some of those modules; you’ll see how to use them to

get the architecture described in Chapter 4.

More specifically, you’ll need modules for the following parts:

• HTTP request and response handling: This is the most basic feature.

As you’re about to see, there are plenty of options out there to pick

from.

• Routes handling: Aside from the preceding, request handling is one of

the most important and crucial parts of our system.

• Pre-processing chain (middleware): You can leave out post-processing

because it’s a less common feature, but pre-processing (or middleware)

is common and very useful.

• Up-to-date documentation: is wasn’t part of our architecture, but I

did mention it in Chapter 2, when I talked about good practices. And

it so happens that there is a module that will help here, so you might

as well add it.

• Hypermedia on the response: Again, not part of the architecture, but

part of a REST, so you’ll add it using the HAL standard.

• Response and request format validation: Finally, this will be an added

bonus; as a good practice, always validate the format of the requests

and responses.

122

Our Alternatives

Instead of looking at each point individually, you’ll take a look at each of the modules,

and I’ll evaluate them accordingly. Some of them, as you’ll see, handle more than just

one thing, which sometimes comes in handy because getting unrelated modules to work

together is not always an easy task.

Request/Response Handling

Regarding request and response handling, they usually both come in the same module.

They are the basics of every HTTP application you intend to make. If you don’t know

how to handle the HTTP protocol, you can’t move forward.

And because Node.js is such a good fit for HTTP applications, there are quite a few

modules that will help you in this task. You need something that can do the following:

• Listen on a specific port for HTTP traffic

• Translate the HTTP message into a JavaScript object so that you can

read it and use it without having to worry about parsing it or about

any of the details of the HTTP protocol

• Write an HTTP response without having to worry about the HTTP

message format

Writing code that listens in a specific port for HTTP traffic is simple; actually, Node.js

provides all the tools you need, out of the box, to achieve the three preceding points. Then

why do we need extra modules if we can easily do it ourselves? That’s a very valid question,

and to be honest, it all depends on your needs. If the system you’re building is small enough,

then it might be a good idea to build the HTTP server yourself; otherwise, it’s always good

to use a well-tested and tried module. These modules also solve other related issues for you,

such as routes handling, so going with a third-party module might be a good choice.

Routes Handling

Routes handling is tightly coupled with request and response handling; it’s the next step

in the processing of the request. Once you translate the HTTP message into an actual

JavaScript object that you can work with, you need to know which piece of code needs to

handle it. This is where routes handling comes in.

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123

There are two sides to this part. First, you need to be able to set up the routes in your

code and associate the handler’s code with one or more specific routes. And then the

system needs to grab the route of the requested resource and match it to one of yours.

That might not be such an easy task. Remember that most routes in any complex system

have parameterized parts for things like unique IDs and other parameters. For example,

take a look at Table5-1.

Usually, routing frameworks provide some sort of templating language that allows

developers to set up named parameters in the route template. Later the framework will

match the requested URLs to the templates, taking into consideration those variable

parts added. Different frameworks add different variations of this; you’ll see some of

them in a bit.

Middleware

This is the name that the pre-processing chain normally gets in the Node.js world, and

that is because the Connect

1

framework (which is the framework on which most other

web frameworks are based) has this functionality.

I already talked about this topic in the previous chapter, so let’s look at some

examples (Listing 5-1) of middleware functions that are compatible with Connect-based

frameworks:

Table 5-1. Routing Example

This… .... Needs to Match This

/v1/books/1234412 /v1/books/:id

/v1/authors/jkrowling/books /v1/:author_name/books

1

See https://www.npmjs.com/package/connect.

CHAPTER 5 WORKING WITHMODULES

124

Listing 5-1. Examples of Middleware Functions

//Logs every request into the standard output

function logRequests(req, res, next) {

console.log("[", req.method, "]", req.url)

next()

}

/*

Makes sure that the body of the request is a valid json object, otherwise,

it throws an error

*/

function formatRequestBody(req, res, next) {

if(typeof req.body == 'string') {

try {

req.body = JSON.parse(req.body)

} catch (ex) {

next("invalid data format")

}

next()

}

The two examples from Listing 5-1 are different, but at the same time they share a

common function signature. Every middleware function receives three parameters: the

request object, the response object, and the next function. The most interesting bit here

is the last parameter, the next function, calling it is mandatory unless you want to end the

processing chain right there. It calls the next middleware in the chain, unless you pass in

a value, in which case it’ll call the first error handler it finds and it’ll pass it the parameter

(normally an error message or object).

The use of middleware is very common for things like authentication, logging,

session handling, and so forth.

CHAPTER 5 WORKING WITHMODULES

125

Up-to-Date Documentation

As I’ve already discussed, keeping up-to-date documentation of the API’s interface

is crucial if you want developers to use your system. I’ll go over some modules that

will help in that area. There is no silver bullet, of course; some of modules add more

overhead than others, but the main goal is to have some sort of system that updates its

documentation as automatically as possible.

Hypermedia ontheResponse

If you want to follow the REST style to the letter, you need to work this into your system.

It is one of the most forgotten features of REST—and a great one, since it allows for self-

discovery, another characteristic of a RESTful system.

For this particular case, you’ll go with a pre-defined standard called HAL (covered

in Chapter 1), so you’ll be checking out some modules that allow you to work with this

particular format.

Response andRequest Validation

I’ll also go over some modules that will let you validate both the response and the

request format. Our API will work with JSON alone, but it’s always useful to validate the

structure of that JSON in the request due to errors in the client application and in the

response to ensure that there are no errors in the server side after code changes.

Adding a validation on every request might be too big of an overhead, so an

alternative might be a test suite that takes care of doing the validation when executed.

But the request format validation will have to be done on every request to ensure that the

execution of your system is not tainted by an invalid request.

The List ofModules

Now let’s go over some modules that take care of one or several of the categories

mentioned; for each one, you’ll list the following attributes:

• The name of the module

• e category it ts into

• e currently released version

CHAPTER 5 WORKING WITHMODULES

126

• A small description

• e home page URL

• e installation instructions

• Code examples

We won’t compare them because it’s not an easy thing to do considering that some

modules only handle one thing, whereas others take care of several things. So after

going over them, I’ll propose a combination of these modules, but you will have enough

information to pick a different combo if it better fits your problem.

HAPI

HAPI is a framework used for building both applications and services (APIs). It’s actively

maintained and has more than half a million downloads a month.

Table5-2 shows more details about this particular framework.

Table 5-2. HAPI Module Information

Category Request/Response handler, Routes handler

Current version 17.4.0

Description HAPI is a conguration-centric web framework designed to create any kind of

web application, including APIs. The main goal of HAPI is to allow developers to

focus on coding the logic of an application, leaving infrastructure code to the

framework.

Home page URL http://hapijs.com/

Installation Installing the framework is simple using npm:

$ npm install hapi

That’s it. HAPI is installed in your application. You can also run the following

command to get the dependency added automatically to your package.json le:

$ npm install hapi --save

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127

Code Examples

After installation, the most basic thing you can do to initialize the system and get

your server up and running is shown in Listing 5-2.

Listing 5-2. Simple Server Code with HAPI.JS

'use strict';

const Hapi=require('hapi');

// Create a server with a host and port

const server=Hapi.server({

host:'localhost',

port:8000

});

// Start the server

async function start() {

try {

await server.start();

}

catch (err) {

console.log(err);

process.exit(1);

}

console.log('Server running at:', server.info.uri);

}

start()

As you can see, this example is quite basic, but the steps required to initialize the

application are there. The server.start line initializes a server object with the new

connection selected. That means you could maintain several open connections at the

same time, as shown in Listing 5-3.

After executing the code from Listing 5-2, you get the following line:

Server running at: http://localhost:8000

And if you try to browse to http://localhost:8000, all you’ll get is the response

from Figure5-1, which is absolutely normal, because even though you’ve created a web

server, you haven’t registered any routes yet.

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128

Listing 5-3. Example of Two Different Servers Being Started on Different Ports

'use strict';

const Hapi=require('hapi');

// Create a server with a host and port

const server=Hapi.server({

host:'localhost',

port:8000

});

const adminServer = Hapi.server({

host: 'localhost',

port: 8001

});

// Add a route to list users

adminServer.route({

method:'GET',

path:'/users',

handler:function(request,h) {

//your code here

}

});

Figure 5-1. 404 error from HAPI.JS

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129

// Start the server

async function start() {

try {

await server.start();

await adminServer.start();

}

catch (err) {

console.log(err);

process.exit(1);

}

console.log('Servers running at: ', server.info.uri, ' and ',

adminServer.info.uri);

}

start()

This code initializes the application, which in turn sets up two different servers: one

for the API itself and another one for an admin system. In this code you can also see how

easy it is to set up routes with HAPI.Although the code can clearly be cleaned up and the

routes definitions can be taken out to a separate file, this is a great example of how two

(or more!) servers with their respective routes can be configured using this framework.

Another interesting bit that HAPI provides is the route templates you can use by

setting up your own. With it, you can use named parameters as seen in Listing 5-4.

Listing 5-4. Setting Up Routes with URL Templating in HAPI.JS

'use strict'

const Hapi = require('hapi');

const server = new Hapi.Server({

host: 'localhost',

port: 3000

});

const getAuthor = (request, reply) => {

// here the author and book parameters are inside

// request.params

};

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130

server.route({

path: '/{author}/{book?}',

method: 'GET',

handler: getAuthor

});

In the code from Listing 5-4, when setting up the route, anything that’s inside curly

brackets is considered a named parameter. The last parameter though, has a ? added to

it, which means it’s optional.

Note Only the last named parameter can be set as optional; otherwise, it makes

no sense.

In addition to the ?, you can use another special character to tell HAPI the number of

segments a named parameter should match; that character is the * and it should be followed

by a number greater than 1, or nothing, if you want it to match any number of segments.

Note Just like the ? character, only the last parameter can be configured to

match any number of segments.

Listing 5-5 shows some examples.

Listing 5-5. Multid-Segment Parameters Example

server.route({

path: '/person/{name*2}', // Matches '/person/john/doe'

method: 'GET',

handler: getPerson

});

server.route({

path: '/author/{name*}', // Matches '/author/j/k/rowling' or

'/author/frank/herbert' or /author/

method: 'GET',

handler: getAuthor

});

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131

function getAuthor(req, reply) {

// The different segments can be obtained like this:

let segments = req.params.name.split('/')

//the rest of your code goes here...

}

function getPerson(req, reply) {

let segments = req.params.name.split(''/')

//the rest of your code here...

}

Express.js

This is one of the most common and used frameworks for Node. As you’re about to see, it

provides all the required building blocks for creating both web apps, and microservices.

Table5-3 shows more details about this framework.

Code Examples

Express.js is sometimes considered the de facto solution when it comes to building a

web application in Node.js, much like Ruby on Rails was for Ruby for a long time.

That being said, it doesn’t mean Express.js should be the only choice or that it is right

choice for every project; so make sure that you are well-informed before choosing a web

framework for your project.

Table 5-3. Express.js Module Information

Category Request/Response handler, Routes handler, Middleware

Current version 4.16.3

Description Express is a full-edged web framework providing small and robust tools for

HTTP servers, making it a great candidate for all kinds of web applications,

including RESTful APIs.

Home page URL http://expressjs.com

Installation $ npm install express

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This particular framework has evolved over the years, and now in version 4 it

provides a generator. To initialize the entire project, you first have to install it with the

following line:

$ npm install express-generator -g

After the installation is complete, you can use the following line:

$ express ./express-test

This line will generate an output like the one shown in Figure5-2.

Figure 5-2. Output of the express generator command

CHAPTER 5 WORKING WITHMODULES

133

The framework generates a lot of folders and files, but in general, it’s the structure

for a generic web application, one that has views, styles, JavaScript files, and other web

app–related resources. This is not for us since we’re building a RESTful API.You’ll want

to remove those folders (views and public, more specifically).

To finalize the process, just enter the folder and install the dependencies; this will

leave you with a working web application. Check Listing 5-6 if you’re curious about

what it takes to initialize the framework (this is all created by Express as part of the init

command).

Listing 5-6. Content of the app.js File Generated by Express

var express = require('express');

var path = require('path');

var favicon = require('serve-favicon');

var logger = require('morgan');

var cookieParser = require('cookie-parser');

var bodyParser = require('body-parser');

var index = require('./routes/index');

var users = require('./routes/users');

var app = express();

// view engine setup

app.set('views', path.join(__dirname, 'views'));

app.set('view engine', 'jade');

// uncomment after placing your favicon in /public

//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));

app.use(logger('dev'));

app.use(bodyParser.json());

app.use(bodyParser.urlencoded({ extended: false }));

app.use(cookieParser());

app.use(express.static(path.join(__dirname, 'public')));

app.use('/', index);

app.use('/users', users);

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134

// catch 404 and forward to error handler

app.use(function(req, res, next) {

var err = new Error('Not Found');

err.status = 404;

next(err);

});

// error handler

app.use(function(err, req, res, next) {

// set locals, only providing error in development

res.locals.message = err.message;

res.locals.error = req.app.get('env') === 'development' ? err : {};

// render the error page

res.status(err.status || 500);

res.render('error');

});

module.exports = app;

Let’s now take a look at Listing 5-7 and what it takes to set up a route in Express.js.

Listing 5-7. All That’s Needed Is Just a Few Lines of Code

const express = require("express");

const app = express()

//...

app.get('/', (req, res) => {

console.log("Hello world!")

})

That’s it. All that you need to remember when setting up a route is the following:

app.VERB(URL-TEMPLATE, HANDLER-FUNCTION). The handler function will receive

three parameters: the request object, the response object, and the next function. The last

parameter is only useful when you set up more than one handler for the same route and

method combination; that way you can chain the methods like they are middleware.

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135

Take a look at the following example in Listing 5-8:

Listing 5-8. Chaining Verbs to the Same URI

app.route('/users/:id')

.all(checkAuthentication)

.all(loadUSerData)

.get(returnDataHandler)

.put(updateUserHandler)

In the preceding code, there are several interesting things happening:

• A named parameter is used for the ID of the user.

• Two middleware functions are set up for every verb hitting the

'/users/:id' route.

• It’s setting up a handler for the GET method hitting the URL, and at

the same time, it’s setting up a handler for when the verb is PUT—all

in the same line of code.

Express provides its own flavor of named parameters (you saw an example of that

in the preceding code), but there are other things you can do. For instance, you can use

regular expressions.

The code from Listing 5-9 matches both '/commit/5bc2ab' and

'/commit/5bc2ab..57ba31', and you can see that getting the parameter inside the

handler’s code is simple too.

You can also set a callback function to do some processing when a specific named

parameter is received (as seen in Listing 5-10); for instance:

Listing 5-9. Example Showing the Use of Regular Expressions to Define a Route

router.get(/^\/commit\/(\w+)(?:\.\.(\w+))?$/, (req, res) => {

let from = req.params[0];

let to = req.params[1] || 'HEAD';

res.send('commit range ' + from + '..' + to);

});

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136

Listing 5-10. Cleaner Code Using Parameter-Specific Callbacks

const router = express.Router()

const express = require('express')

const app = express()

router.param('user_id', (req, res, next, id) => {

loadUser(id, function(err, usr) {

if(err) {

next(new Error("There was an error loading the user's

information")) //this will call erorr handler

} else {

req.user = usr

next()

}

})

//then on the route definition

app.get('/users/:user_id', (req, res) => {

//req.user is already defined and can be used

})

If there is an error on the user_id callback function, then the route’s handler will

never be called, because the first error handler will be called instead.

Finally, let’s look at some examples of middleware usage inside Express.js. I already

covered the basics for this type of function earlier, but you never saw how to use it with

Express.js.

You can do it in two ways: set up a global middleware (Listing 5-11) or a route-specific

middleware (Listing 5-12).

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137

For a global middleware, you just do this:

Listing 5-11. Middleware Example

app.use((req, res, next) => {

//your code here will be executed on every request

next() //remember to call next unless you want the chain to end here.

})

For a route-specific middleware, you do this:

Listing 5-12. Route-Specific Middleware Syntax

app.use('/books', (req, res, next) => {

//this function will only be called on this path

next() //always important to call next unless you don't want the

process' flow to continue.

})

You can even set up a route-specific stack of middleware, as seen in Listing 5-13.

Listing 5-13. Example of a Stack of Middleware for a Specific Store

app.use('/books', function(req, res, next){

//this function will only be called on this path

next() //always important to call next unless you don't want the

process' flow to continue.

}, function(req, res, next) {

//as long as you keep calling next, the framework will keep advancing

in the chain until reaching the actual handler

next()

})

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138

Restify

You can think of Restify as a version of ExpressJS tailored to only be able to create

RESTful APIs. Table5-4 shows more details about this framework.

Code Examples

Restify borrows a lot of its features from Express, so I’ll focus on the things that it adds;

for other examples, please refer to the previous module or visit the Restify home page.

Initialization is simpler than with Express, although there are no code generators.

The following code is all you need to start up a server:

Listing 5-14. Simple Web Server Creation with Restify

const restify = require('restify');

let server = restify.createServer({

});

server.listen(8080);

Table 5-4. Restify Module’s Information

Category Request/Response handler, Routes handler, Middleware

Current version 6.3.4

Description Restify is a framework specically designed for building REST APIs. It

borrows heavily from Express.js (specically, versions prior to 4.0) because

Express is considered the standard when it comes to building web apps.

Home page URL http://restify.com/

Installation $ npm install restify

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139

The createServer method provides some helpful options that will simplify your job

in the future. Table5-5 lists some of Restify’s options.

In the most basic ways, routes are handled just like Express: you can either pass in

the path template and the route handler, or you can pass in a regular expression and the

handler.

In a more advanced way, Restify provides some goodies that Express doesn’t. The

following subsections provide some examples.

Naming Routes

You can set up names for specific routes, which will in turn allow you to jump from one

handler to others using that attribute. Let’s look at how to set up the names first.

Listing 5-15. Sample Code Showing How to Set Up Named Routes

server.get('/foo/:id', (req, res, next) =>

next('foo2')

);

server.get({

Table 5-5. List of Restify Options

Option Description

certicate For building HTTPS servers, pass in the path to the certicate here.

key For building HTTPS servers, pass in the path to the key le here.

log Optionally, you can pass in an instance of a logger. It needs to be an instance of node-

bunyan.

2

name The name of the API.Used to set the server response header; by default it is “restify.”

version A default version for all routes.

formatters A group of content formatters used for content-negotiation

2

See https://github.com/trentm/node-bunyan.

CHAPTER 5 WORKING WITHMODULES

140

path: '/foo/:id'

}, (req, res, next) => {

res.send(200);

next();

});

This code is setting up two different handlers for the same path, but Restify will only

execute the first handler it finds, so the second one will never get executed unless the

next statement is called with the name of the second route.

Naming is also used to reference routes when rendering the response, which allows

for an interesting feature: hypermedia on the response. To be honest, the solution

proposed by Restify is a bit basic and it doesn’t really provide a good mechanism for

automatically adding hypermedia for self-discovery, but it is more than most other

frameworks do. Listing 5-16 shows an example of how it works.

Listing 5-16. Hypermedia on the Response Basic Example

const restify = require("restify")

let server = restify.createServer()

server.get({

path: '/country/:id/cities'

}, (req, res, next) => {

res.send('cities') //no need to call the next function, we don't want

to add anything after this step

})

server.get('/country/:id', function(req, res, next) {

res.send({

cities: server.router.render('country-cities', {id: "uruguay"})

})

server.listen(3000)

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141

The example is quite basic, but it provides the required logic to understand that there

is no need to know the URL structure needed to get a list of cities for a specific country

from within the /countries/:id endpoint, which in turn provides easier maintenance if,

in the future, that first URL needs to be changed.

Versioning Routes

Restify provides support for a global version number, as you saw earlier, but it also

provides the ability to have different versions on a per-route basis. And, it also provides

support for the Accept-version header to pick the right route.

Note If the header is missing, and more than one version for the same route is

available, then Restify will pick the first one defined in the code.

Listing 5-17 shows how to do it.

Listing 5-17. Route Versioning with Restify

function respV1(req, res, next) {

res.send("This is version 1.0.2")

}

function respV2(req, res, next) {

res.send("This is version 2.1.3")

}

let myPath = "/my/route"

server.get({path: myPath, version: "1.0.2"}, respV1)

server.get({path: myPath, version: "2.1.3"}, respV2)

Now, when hitting the path with different values for Accept-version, the information

in Table5-6 is what you get.

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142

Content Negotiation

Another interesting feature that Restify provides is support for content negotiation.

All you need to do to implement this feature is provide the right content formatters

during initialization, like in Listing 5-18.

Listing 5-18. Content Negotiation Example

restify.createServer({

formatters: {

'application/foo; q=0.9': (req, res, body) => {

if (body instanceof Error)

return body.stack;

if (Buffer.isBuffer(body))

return body.toString('base64');

return util.inspect(body);

}

})

Table 5-6. Examples of Content Negotiation

Version Used Response Description

This is version 1.0.2 No version was used, so by default, the server

is picking the rst one dened.

~1 This is version 1.0.2 Version 1.x.x was selected, so that is what the

server responds with.

~3 {

“code”: “InvalidVersion”,

“message”: “GET /my/route

supports versions: 1.0.2, 2.1.3”

}

An error message is returned when an

unsupported version is requested.

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143

Note By default, Restify comes bundled with formatters for application/json, text/

plain, and application/octet-stream.

There are other minor features provided by Restify that I’m not covering, so please

refer to the official web site for information.

Vatican.js

Vatican.js is an attempt at creating an easy-to-use and boilerplate-based library, which

can reduce the coding time while working on RESTful APIs. When you’re starting to work

on your API’s code, there are a lot of repeated tasks that you need to perform over and

over, until you have all your endpoints set up, and your models, and so on. This library

attempts to remove all that work by generating most of it automatically. Table5-7 shows

more details about the framework.

Code Examples

After installation, Vatican.js provides a command-line script to create the project and

add resources and resource handlers to it. So to get the project started, you’ll need to use

the following command:

$ vatican new test_project

Table 5-7. Vatican.js Module Information

Category Request/Response handler, Middleware, Routes handling

Current version 1.5.0

Description Vatican.js is another attempt of a framework designed to create RESTful

APIs. It doesn’t follow the Express/Restify path. Its focus is more on the

MVP stage of the API, but it provides an interesting alternative.

Home page URL https://github.com/deleteman/vatican

Installation $ npm install –g vatican

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144

The preceding code generates the output shown in Figure5-3.

The main file (index.js) has the content in Listing 5-19.

Listing 5-19. Default index.js Generated by Vatican.js.

var Vatican = require("vatican")

//Use all default settings

var app = new Vatican()

app.dbStart(function() {

console.log("Db connection stablished...")

//Start the server

app.start()

} )

Vatican comes with MongoDB integration, so the dbStart method is actually a

reference to the connection to the NoSQL storage. By default, the server is assumed to be

in localhost and the database name used is vatican-project.

The default port for Vatican is 8753, but just like all defaults in Vatican, it can be

overwritten during the instantiation stage. These are the options that can be passed in to

the constructor, as shown in Table5-8.

Figure 5-3. Output of the Vatican.js generate action

CHAPTER 5 WORKING WITHMODULES

145

Table 5-8. List of Options for the Vatican.js Constructor

Option Description

port Port of the HTTP server

handlers Path to the folder where all handlers are stored. By default it’s ./handlers

db Object with two attributes: host and dbname

cors This is either a Boolean indicating whether CORS is supported by the API or an object

indicating each of the supported headers.

Setting up a route in Vatican is also a bit different than the others; the command-

line script provides the ability to autogenerate the code for the entity/model file and the

controller/handler file, which also includes basic code for the CRUD operations.

To autogenerate the code, use the following command from within the project’s

folder:

$ vatican g Books -a title:string description:string copies:int -m

newBook:post listBooks:get removeBook:delete

This line outputs something like what’s shown in Figure5-4.

It basically means that Vatican created both the handler file and the entity (inside the

schemas folder). If you check the handler’s file, you’ll notice how all the actions already

have their code in there; that’s because Vatican was able to guess the meaning of the

actions provided in the command line by using their name.

• newBook: Using “new” assumes you’re creating a new instance of the

resource.

• listBooks: Using “list” assumes you want to generate a list of items.

• removeBook: Using “remove” assumes you’re trying to remove a

resource.

Figure 5-4. Output of the resource generator command

CHAPTER 5 WORKING WITHMODULES

146

Variations of those words are also valid, and Vatican will use them to guess the code.

You can now go ahead and start the server; the endpoints will work and save information

to the database.

One final comment on resource generation is about routing; you haven’t specified

any routes yet, but Vatican has created them anyway. Inside the handler file, you’ll notice

annotations as shown in Listing 5-20.

Listing 5-20. Generated Code for New REST Methods with Endpoint Definition

Included

module.exports = class BooksHdlr {

constructor(model, dbModels) {

this.model = model;

this.dbModels = dbModels;

}

@endpoint (url: /books method: post)

newBook(req, res, next) {

var data = req.params.body

//...maybe do validation here?

this.model.create(data, function(err, obj) {

if(err) return next(err)

res.send(obj)

})

}

@endpoint (url: /books method: get)

listBooks(req, res, next) {

var page = null,

size = null

if(req.params.query.page || req.params.query.size) {

page = req.params.query.page || 0

size = req.params.query.size || 10

}

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147

var query = {}

var finder = this.model.find(query)

if(page !== null && size !== null) {

finder

.skip(page * size)

.limit(size)

}

finder.exec(function(err, list) {

if(err) return next(err)

res.send(list)

})

}

@endpoint (url: /books method: delete)

removeBook(req, res, next) {

var id = req.params.query.id || req.params.url.id ||

req.params.body.id

this.model.remove({_id: id}, function(err) {

if(err) return next(err)

res.send({success: true})

});

}

The annotations in the preceding example on the method’s definition are not

standard JavaScript, but Vatican is able to parse them and turn them into data during

boot up. That means that with Vatican there is no routes file; each route is defined above

its associated method, and if you want to get a full list of routes for your system, you can

use the following command line:

$ vatican list

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148

And it’ll produce the output shown in Figure5-5, which lists for every handler all the

routes with the method, the path, the file, and the associated method name.

Note The annotations can be commented out with a single line comment (//) to

avoid your editor/linter from complaining about the construct; even then, Vatican.js

will be able to parse it.

Finally, Vatican also fits inside the middleware category, and that’s because even

though it’s not based on Connect or Express, it does support Connect-based middleware.

The only difference is the method name that uses it.

Listing 5-21. Middleware Usage Example

vatican.preprocess(middlewareFunction) //generic middleware for all routes

vatican.preprocess(middelwareFunction, ['login', 'authentication'])

//middleware for two routes: login and authentication.

To set the name of a route, you can add that parameter in the annotation, like in

Listing 5-22.

Listing 5-22. Setting Up Named Routes Using Annotations

@endpoint(url: /path method: get name: login)

There are still some more features that Vatican.js provides. To read about them,

please refer to the official web site.

swagger-node-express

This module bridges the gap between Swagger and Express, allowing you to auto-

document your express APIs easily. Table5-9 shows more details about it.

Figure 5-5. Output from the list command

CHAPTER 5 WORKING WITHMODULES

149

Code Examples

The first thing you need to do after you install the module is integrate Swagger into

your Express app. Listing 5-23 provides the code to do that.

Listing 5-23. First Steps After Installing swagger-node-express

// Load module dependencies.

const express = require("express")

, app = express()

, bodyParser = require("body-parser")

, swagger = require("swagger-node-express").createNew(app);

// Create the application.

app.use(express.json());

app.use(bodyParser.urlencoded({extended: true}));

After integration is done, the next thing to do is add the models and the handlers.

The models are in the form of JSON data (where this is defined is left to the preference of

the developer). The handlers contain the actual code of the route handlers, along with

other descriptive fields that act as documentation.

Table 5-9. swagger-node-express Module Information

Category Up-to-date documentation

Current version 2.1.3

Description This is a module for Express. It integrates into an Express app and provides the

functionalities that Swagger

3

does for documenting APIs, which is a web interface

with documentation of each method and the ability to try these methods.

Home page URL https://github.com/swagger-api/swagger-node

Installation $ npm install swagger-node-express

3

See http://swagger.io/.

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150

Listing 5-24 is an example of a model definition.

Listing 5-24. Model Definition Using Simple JSON Format

exports.models = {

"Book": {

"id": "Book",

"required": ["title", "isbn"],

"properties": {

"title": {

"type": "string",

"description": "The title of the book"

},

"isbn": {

"type": "string",

"description": "International Standard

Book Number"

},

"copies": {

"type": "integer",

"format": "int64",

"description": "Number of copies of the

book owned by the bookstore"

}

In Listing 5-24, the format used is JSON Schema

4

and it might be tedious to maintain,

but it provides a standard way for Swagger to understand how our models are created.

4

See http://json-schema.org/.

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151

Tip Manually maintaining a lot of model descriptions might be too much work,

and it’s prone to generate errors in the documentation, so it might be a good idea

to either use the description to autogenerate the code of the model or autogenerate

the description from the model’s code.

Once the model description is done, you add it to Swagger, as deomstrated in

Listing 5-25.

Listing 5-25. Letting Swagger Know About Your Models

// Load module dependencies.

const express = require("express")

, swagger = require("swagger-node-express")

, models = require('./models-definitions').models

//....

swagger.addModels(models)

Now you move on to the handler’s description, which contains fields describing each

method, and the actual code to execute.

Listing 5-26. Handler’s Code and Documentation Definition and Setup

const swagger = require("swagger-node-express");

//Book handler's file

exports.listBooks = {

"spec": {

"description": "Returns the list of books",

"path": "/books.{format}",

"method": "GET",

"type": "Book",

"nickname": "listBooks",

"produces": ["application/json"],

"parameters": [swagger.paramTypes.query("sortBy",

"Sort books by title or isbn", "string")]

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152

},

"action": (req, res) => {

//...

}

//main file's code

var bookHandler = require("./bookHandler")

//...

swagger.addGet(bookHandler.listBooks) // adds the handler for the list

action and the actual action itself

This code shows how to describe a specific service (a list of books). Again, some of

these parameters (inside the spec object) can be autogenerated; otherwise, manually

maintaining a lot of specs can lead to outdated documentation.

Finally, set up the URLs for the Swagger UI (which will display the documentation

and will also provide the UI to test the API) and the version, as shown in Listing 5-27.

Listing 5-27. Letting Swagger Know Its UI’s URL

swagger.configure("http://myserver.com", "0.1")

Let’s now look at Listing 5-28, a complete example of a main file, showing the setup

and configuration of Swagger and the Swagger UI.

5

Listing 5-28. Full Example of Swagger-Express Integration

// Load module dependencies.

const express = require("express")

, models = require("./models-definitions").models

, app = express()

, bodyParser = require("body-parser")

, booksHandler = require("./booksHandler") //load the handler's definition

, swagger = require("swagger-node-express").createNew(app) //bundle the app

to swagger

5

See https://github.com/swagger-api/swagger-ui.

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153

// Create the application.

app.use(express.json());

app.use(bodyParser.urlencoded({extended: true}));

var static_url = express.static(__dirname + '/swagger-ui') //the swagger-ui

is inside the "swagger-ui" folder

swagger.configureSwaggerPaths("", "api-docs", "") //you remove the {format}

part of the paths, to simplify things

app.get(/^\/docs(\/.*)?$/ , (req, res, next) => {

if(req.url === '/docs') {

res.writeHead(302, {location: req.url + "/"})

res.end()

return

}

req.url = req.url.substr('/docs'.length)

return static_url(req, res, next)

})

//add the models and the handler

swagger

.addModels(models)

.addGet(booksHandler.listBooks)

swagger.configure("http://localhost:3000", "1.0.0")

app.listen("3000")

Note Before trying out this code, you’ll have to copy the folder called “swagger-ui”

inside the module’s folder, into your project’s root folder (or whatever you set the

static_url variable to).

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154

Figure 5-6. The generated UI

Figure5-6 is a screenshot of the resulting UI that you get by visiting

http://localhost:3000/docs.

I/ODocs

Another option when it comes to self-documenting APIs is I/O Docs, which, although in

the end provides similar results to Swagger, also offers quite a different approach getting

there.

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155

Table5-10 shows the details on this particular project, as well as the steps required to

install it.

Code Examples

After installation is done, the only thing left to do to test the application is create a

configuration file; there is a config.json.sample file you can use as a starting point.

Tip You can copy the config.json.sample file using the cp command like so: cp

config.json.sample config.json . By doing that, you immediately have a

valid config file to start using.

To start up the documentation server, you’ll first need to start your redis server and

then use one of the following commands:

$ redis-server #preferabliy you'll do this in another console, since this

is a blocking operation

$ npm start #for *nix and OSX systems

C:\your-project-folder> npm startwin #for Windows systems

After that, use your browser to go to http://localhost:3000 to start testing the

documentation system.

Table 5-10. I/O Docs Module Information

Category Up-to-date documentation

Current Version N/A

Description I/O Docs is a live documentation system designed for RESTful APIs. By

dening the API using the JSON Schema, I/O Docs generates a web

interface to try out the API.

Home page URL https://github.com/mashery/iodocs

Installation $ git clone http://github.com/mashery/iodocs.git

$ cd iodocs

$ npm install

CHAPTER 5 WORKING WITHMODULES

156

Tip If you get a login modal the first time you visit that URL, just hit ENTER (with

empty credentials) and you’ll be logged in.

Figure5-7 is a screenshot of one of the sample APIs already configured.

As you can see in Figure5-7, when the methods are tested, a response is shown

underneath. If you want to set up your own API, there are a few things to do:

1. Add your API to the list of documented APIs inside public/data/

apiconfig.json like in Listing 5-29.

Figure 5-7. The default UI when trying out methods

CHAPTER 5 WORKING WITHMODULES

157

Listing 5-29. Adding Your API’s Entry to the List of Docummented APIs

{

"klout": {

"name": "Klout v2 API"

},

"egnyte": {

"name": "Egnyte API"

},

"usatoday": {

"name": "USA TODAY Census API"

},

"foursquare": {

"name": "Foursquare (OAuth 2.0 Auth Code)"

},

"rdio": {

"name": "Rdio Beta (OAuth 2.0 Client Credentials)"

},

"rdio2": {

"name": "Rdio Beta (OAuth 2.0 Implicit Grant)"

},

"requestbin": {

"name": "Requestb.in"

},

"bookstore": {

"name": "Dummy Bookstore API"

}

2. Create a new le called bookstore.json and store it inside the

public/data folder. is new JSON le will contain the description

of your API and the methods in it; something like shown in

Listing 5-30.

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158

Listing 5-30. The Full JSON Definition of Your API’s Endpoints

{

"name": "Dummy Bookstore API",

"description": "Simple bookstore API",

"protocol": "rest",

"basePath": "http://api.mybookstore.com",

"publicPath": "/v1",

"auth": {

"key": {

"param": "key"

}

},

"headers": {

"Accept": "application/json",

"Foo": "bar"

},

"resources": {

"Books": {

"methods": {

"listBooks": {

"name": "List of books",

"path": "/books",

"httpMethod": "GET",

"description": "Returns the list of books in stock",

"parameters": {

"sortBy": {

"type": "string",

"required": false,

"default": "title",

"description": "Sort the results by title

or ISBN code"

}

},

CHAPTER 5 WORKING WITHMODULES

159

"showBook": {

"name": "Show book",

"path": "/books/{bookId}",

"httpMethod": "GET",

"description": "Returns the data of one specific book",

"parameters": {

"bookId": {

"type": "string",

"required": true,

"default": "",

"description": "The ID of the specific

book"

}

3. Start up the documentation server and point your web browser to it.

You’ll see a screen that looks similar to Figure5-8.

CHAPTER 5 WORKING WITHMODULES

160

Figure 5-8. Your custom documentation translated into a web UI

Unlike with Swagger, this documentation system is not meant to be integrated into

your project, so autogenerating the JSON code might be a bit more difficult. The server

does, however, auto-adapt to updates on the JSON file, so you don’t have to restart it

everytime to change something, but you would still have to find a way to easily generate

that JSON definition and copy it into the right folder.

Halson

Halson attempts to simplify the task of adding hypermedia into your response by

providing an object-oriented interface. Table5-11 shows the basic information about

this module, including the steps to install it.

CHAPTER 5 WORKING WITHMODULES

161

Code Examples

The API provided by this module is quite straightforward, and if you’ve read about

the standard,

6

you should have no problem figuring out how to use it.

Listing 5-31 is the example from the readme.

Listing 5-31. Simple Halson Example

const halson = require('halson');

let embed = halson({

title: "joyent / node",

description: "evented I/O for v8 javascript"

})

.addLink('self', '/joyent/node')

.addLink('author', {

href: '/joyent',

title: 'Joyent'

});

let resource = halson({

title: "Juraj Hájovský",

username: "hajovsky",

Table 5-11. Halson Module Information

Category Hypermedia on the response

Current version 3.0.0

Description Halson is a module that helps create HAL-compliant JSON objects, which

you’ll then be able to use as part of the response in your API.

Home page URL http://github.com/seznam/halson

Installation $ npm install halson

6

See http://stateless.co/hal_specification.html.

CHAPTER 5 WORKING WITHMODULES

162

emails: [

"juraj.hajovsky@example.com",

"hajovsky@example.com"

]

})

.addLink('self', '/hajovsky')

.addEmbed('starred', embed);

console.log(JSON.stringify(resource));

The preceding code will output the following:

Listing 5-32. JSON Output Generated by HALSON

{

"title": "Juraj Hájovský",

"username": "hajovsky",

"emails": [

"juraj.hajovsky@example.com",

"hajovsky@example.com"

],

"_links": {

"self": {

"href": "/hajovsky"

}

},

"_embedded": {

"starred": {

"title": "joyent / node",

"description": "evented I/O for v8 javascript",

"_links": {

"self": {

"href": "/joyent/node"

},

CHAPTER 5 WORKING WITHMODULES

163

"author": {

"href": "/joyent",

"title": "Joyent"

}

As you can see, the module successfully abstracted the details about the HAL

standard; all you need to know is how to add links and what an embedded object is.

HAL

Just like HALSON, this module creates the representation of Hypermedia linking your

resources, which can then be added to your own API’s response.

You can read the basic information about the module in Table5-12.

Code Examples

The API of this module is simpler than the one provided by HALSON and it also

provides XML encoding (remember that even though you’re not focusing on XML, it can

be a possible second representation for your resources).

Table 5-12. HAL Module Information

Category Hypermedia on the response

Current version 1.2.0

Description HAL is an alternative to HALSON.It provides a simpler interface but the same

underlying functionality: abstracting the HAL+JSON format and giving the

developer an easy way to use it.

Home page URL https://www.npmjs.com/package/hal

Installation $ npm install hal

CHAPTER 5 WORKING WITHMODULES

164

Listing 5-33 provides a simple example following our bookstore theme.

Listing 5-33. Simple Example of Adding a List of Objects Embedded into a Parent

const hal = require('hal');

let books = new hal.Resource({name: "Books list"}, "/books")

let listOfBooks = [

new hal.Resource({id: 1, title: "Harry Potter and the Philosopher's

stone", copies: 3}, "/books/1"),

new hal.Resource({id: 2, title: "Harry Potter and the Chamber of

Secrets", copies: 5}, "/books/2"),

new hal.Resource({id: 3, title: "Harry Potter and the Prisoner of

Azkaban", copies: 6}, "/books/3"),

new hal.Resource({id: 4, title: "Harry Potter and the Goblet of Fire",

copies: 1}, "/books/4"),

new hal.Resource({id: 5, title: "Harry Potter and the Order of the

Phoenix", copies: 8}, "/books/5"),

new hal.Resource({id: 6, title: "Harry Potter and the Half-blood Prince",

copies: 2}, "/books/6"),

new hal.Resource({id: 7, title: "Harry Potter and the Deathly Hollows",

copies: 7},"/books/7")

]

books.embed('books', listOfBooks)

console.log(JSON.stringify(books.toJSON()))

This code will output the JSON code in Listing 5-34.

Listing 5-34. The JSON Representation of the Relationships Defined in the

Previous Listing

{

"_links": {

"self": {

"href": "/books"

}

},

CHAPTER 5 WORKING WITHMODULES

165

"_embedded": {

"books": [

{

"_links": {

"self": {

"href": "/books/1"

}

},

"id": 1,

"title": "Harry Potter and the Philosopher's stone",

"copies": 3

},

{

"_links": {

"self": {

"href": "/books/2"

}

},

"id": 2,

"title": "Harry Potter and the Chamber of Secrets",

"copies": 5

},

{

"_links": {

"self": {

"href": "/books/3"

}

},

"id": 3,

"title": "Harry Potter and the Prisoner of Azkaban",

"copies": 6

},

CHAPTER 5 WORKING WITHMODULES

166

{

"_links": {

"self": {

"href": "/books/4"

}

},

"id": 4,

"title": "Harry Potter and the Goblet of Fire",

"copies": 1

},

{

"_links": {

"self": {

"href": "/books/5"

}

},

"id": 5,

"title": "Harry Potter and the Order of the Phoenix",

"copies": 8

},

{

"_links": {

"self": {

"href": "/books/6"

}

},

"id": 6,

"title": "Harry Potter and the Half-blood Prince",

"copies": 2

},

{

"_links": {

"self": {

"href": "/books/7"

}

},

CHAPTER 5 WORKING WITHMODULES

167

"id": 7,

"title": "Harry Potter and the Deathly Hollows",

"copies": 7

}

]

},

"name": "Books list"

}

JSON-Gate

JSON validation is useful to ensure that both the requests your API gets and the

responses it provides are always in check against a publicly defined standard. This is

where you can turn to JSON-Gate for help (please see Table5-13 for basic information

about the module).

Code Examples

The usage of this module is quite simple. First, you need to define the schema against

which your objects will be validated. This can be done directly with the createSchema

method or (recommended) in a separate file, and then passed to the validator. After the

schema has been added, you can proceed to validate as many objects as you need.

Table 5-13. JSON-Gate Module Information

Category Request/Response validation

Current version 0.8.23

Description This module validates the structure and content of a JSON object against a

predened schema that follows the JSON Schema format.

Home page URL https://www.npmjs.com/package/json-gate

Installation $ npm install json-gate

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168

Listing 5-35 provides a simple example.

Listing 5-35. Simple Example Showing how to Define a Schema and Validate

Your Input Against It

const createSchema = require('json-gate').createSchema;

let schema = createSchema({

type: 'object',

properties: {

title: {

type: 'string',

minLength: 1,

maxLength: 64,

required: true

},

copies: {

type: 'integer',

maximum: 20,

default: 1

},

isbn: {

type: 'integer',

required: true

}

},

additionalProperties: false

});

let invalidInput = {

title: "This is a valid long title for a book, it might not be the best

choice!",

copies: "3"

}

CHAPTER 5 WORKING WITHMODULES

169

try {

schema.validate(invalidInput);

} catch(err) {

return console.log(err)

}

The code from Listing 5-33 will output the following error:

[Error: JSON object property 'title': length is 71 when it should be at

most 64]

There are two things to note here:

• On one hand, the error message is very “human-friendly.” All the

error messages reported by JSON-Gate are like this, so it’s easy to

understand what you did wrong.

• On the other hand, as you probably noticed, the invalidInput

object has three errors in its format (exceeding length of the title

parameter, invalid type for the copies parameter, and finally, a

missing isbn parameter); the validation stops at the first error, so

correcting multiple problems might be slow because you’ll have to

correct them one at a time.

If you’re not into catching exceptions (and why should you in Node.js?), there is an

alternative to the validate method, which is passing in a second argument—a callback

function with two arguments: the error object and the original input object.

TV4

Just like with the previous module, this one empowers you with the ability to validate

your input and output messages easily. Table5-14 has all the infomation you need to get

you started using TV4.

CHAPTER 5 WORKING WITHMODULES

170

Code Examples

The main difference between this validator and JSON-Gate is that this one is specific

for version 4 of the JSON Schema draft. It also allows you to collect multiple errors

during validation and to reference other schemas, so you can reuse parts of the schema

in different sections.

Let’s look at some examples:

Listing 5-36. Simple Example of Input Validation Using TV4

var validator = require("tv4")

var schema ={

"title": "Example Schema",

"type": "object",

"properties": {

"firstName": {

"type": "string"

},

"lastName": {

"type": "string"

},

"age": {

"description": "Age in years",

"type": "integer",

Table 5-14. TV4 Module Information

Category Request/Response validation

Current version 1.3.0

Description This module provides validation against version 4 of the JSON Schema.

7

Home page url https://www.npmjs.com/package/tv4

Installation $ npm install tv4

7

See http://json-schema.org/latest/json-schema-core.html.

CHAPTER 5 WORKING WITHMODULES

171

"minimum": 0

}

},

"required": ["firstName", "lastName"]

}

var invalidInput = {

firstName: 42,

age: "100"

}

var results = validator.validateMultiple(invalidInput, schema)

console.log(results)

The preceding example will output the following error object:

Listing 5-37. Multiple Error Messages Returned by the Code from Listing 5-34

{ errors:

[ { message: 'Missing required property: lastName',

params: [Object],

code: 302,

dataPath: '',

schemaPath: '/required/1',

subErrors: null,

stack: '......'},

{ message: 'Invalid type: number (expected string)',

params: [Object],

code: 0,

dataPath: '/firstName',

schemaPath: '/properties/firstName/type',

subErrors: null,

stack: '......'},

{ message: 'Invalid type: string (expected integer)',

params: [Object],

code: 0,

dataPath: '/age',

CHAPTER 5 WORKING WITHMODULES

172

schemaPath: '/properties/age/type',

subErrors: null,

stack: '......'}]

missing: [],

valid: false }

The output is much bigger than the one from JSON-Gate and it needs a bit of parsing

before being able to use it, but it also provides quite a lot of information aside from the

simple error message.

For a full reference on the API provided by this validator, please visit its home page.

To understand all the possible validations that can be done using JSON Schema, please

visit the online draft.

8

Summary

This chapter covered a lot of modules that will help you create the perfect API

architecture. You saw at least two modules for every category on options for picking the

tools for the job.

In the next chapter, you’ll define the API that you’ll be developing in the following

chapters, and with that definition, you’ll also pick the set of modules (from the ones we

covered in this chapter) that you’ll use to develop it.

8

See http://json-schema.org/specification.html.

CHAPTER 5 WORKING WITHMODULES

173

F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1_6

CHAPTER 6

Planning Your REST API

You’re almost ready to get your hands dirty and start developing the actual API; but

before you start, let’s apply everything I’ve talked about until this point:

• REST

• Dening what an ideal RESTful architecture should look like

• Good practices when developing an API

• Modules that would help achieve that ideal goal

In this chapter, I’ll set up the ground work for the final development this book will

take you through:

• I’ll define a specific problem to solve.

• You’ll create a written specication for it, writing down the list of

resources and endpoints.

• To help understand how all those resources relate to each other,

you’ll create a UML diagram of our system.

• I’ll go over some options for a database engine, choosing the best one

for our problem.

The final result of this chapter will be all the information you need to start the

development process (covered in the next chapter).

The Problem

In case you haven’t noticed yet, throughout this book, every major (and probably minor,

too) code sample and fake scenario has been done using a bookstore as the root of that

example. This chapter keeps up that trend, so instead of switching into another area,

you’ll dig deeper and flesh-out our fake bookstore.

174

Let’s call our fake bookstore Come&Read and assume that we’ve been asked to

create a distributed API that will bring the bookstore into the twenty-first century.

Right now, it’s a pretty decent business. The bookstore currently has 10 different

points of sale located across the United States—not a lot, but the company leadership

is considering expanding into even more states. The current main problem, though,

is that all of those stores have barely entered the digital era. The way of working and

recordkeeping is very manual and heterogeneous; for instance:

• Some of the smaller stores keep records on paper and send a

manually typed weekly report to the head store.

• While the bigger locations tend to use some sort of CRM software,

there is no standard as long as numbers are exported into a common

format and sent in a weekly report.

• Based on the weekly reports, the head store handles inventory of the

chain-wide matters (store-specic stock, global stock, sales both

per- store and global, employee records, etc.).

• Overall, the bookstore lacks web interaction with its customers,

which a twenty-first century business must have. Its web site only

lists addresses and phone numbers, and nothing more.

Figure6-1 shows an image mapping the current situation of this bookstore chain.

CHAPTER 6 PLANNING YOUR REST API

175

As you can see in Figure6-1, all of the secondary stores are connected by a very thin

line to the main store, which is located in Springfield, IL.

The goal is to grow as a business not only by opening new stores across the country

but by also strengthening the bond between all the stores. And to achieve this, the

backbone of everything will be our API.Our system will have to be a decentralized one,

meaning that you’ll treat the main store just like any other store and provide a common

set of tools and data sources for every client application that might come in the future,

instantly allowing for such things as the following:

• Cross-store searches

• Automatic control of global stock

• Automatic control over sales on a global level

• Dynamic data sources for things like web sites and mobile apps

Figure 6-1. How every store connects to the main store

CHAPTER 6 PLANNING YOUR REST API

176

A new mental image of this bookstore chain might be like the one shown in Figure6- 2.

Figure6-2 shows the new system living in the cloud, with all stores connected

directly to it. The bond is stronger now, since everything is done automatically and every

piece of information is available to all stores. Also, this new API-based system allows

for the easy development of new ways to interact with potential customers, including

mobile apps and dynamic web sites.

Figure 6-2. The new status of the bookstore chain

CHAPTER 6 PLANNING YOUR REST API

177

The Specifications

Now that we know the current situation of the chain and the goal of our system, we

need to start writing some hard specs. These will determine the way the system evolves

and help with planning the development by giving us a better idea of the size of the

project. Specifications also help us spot any design errors before we start with the

implementation.

Note We will not spend much time on the process of writing the system’s specs,

since that subject is beyond the scope of this book. We’ll just lay down the specs

and note anything that might be extremely relevant; the rest will be left to your

understanding of this process.

To provide everything mentioned, the system needs to have the following features:

• Cross-store book search/listing capabilities.

• Storage: is code is in charge of providing the information to all

other entities, as well as talking directly to the data storage system

that you choose.

• Sales: is feature is dedicated to allow for both in-store and online

sales.

• User reviews of books: is will provide a much-needed layer of

interaction between the stores and the potential clients.

• Authentication: This will let employees and customers login into the

system.

Table6-1 describes the resources that we’ll be dealing with in this implementation.

CHAPTER 6 PLANNING YOUR REST API

178

Table 6-1. Resources, Properties, and Basic Descriptions

Resource Properties Description

Books • Title

• Authors

• ISBN Code

• Stores

• Genre

• Description

• Reviews

• Price

This is the main entity; it has all the properties required to

identify a book and to locate it in a specic store.

Authors • Name

• Description

• Books

• Website

• Image/Avatar

This resource is highly related to a book’s resource because

it lists the author of every book in a store.

Stores • Name

• Address

• State

• Phone numbers

• Employees

Basic information about each store, including the address,

employees, and so forth.

Employees • First name

• Last name

• Birthdate

• Address

• Phone numbers

• Email

• HireDate

• EmployeeNumber

• Store

Employee information, contact data, and other internal

properties that may come in handy for an admin type of user.

(continued)

CHAPTER 6 PLANNING YOUR REST API

179

Table 6-1. (continued)

Resource Properties Description

Clients • Name

• Address

• Phone number

• Email

Basic contact information about a client.

BookSales • Date

• Books

• Store

• Employee

• Client

• TotalAmount

The record of a book sale. It can be related to a store sale or

an online sale.

ClientReviews • Client

• Book

• ReviewText

• Stars

The resource in which client reviews about a book are saved.

The client can enter a short free-text review and a number

between 0 and 5 to represent stars.

Note Even though it’s not listed in Table6-1, all resources will have some

database-related attributes, such as id, created_at, and updated_at, which

you’ll use throughout the code.

Based on the resources in Table6-1, let’s create a new table that lists the endpoints

needed for each resource. Table6-2 helps define the functionalities that each resource

will have associated to it.

CHAPTER 6 PLANNING YOUR REST API

180

Table 6-2. List of Endpoints, Associated Parameters, and HTTP Methods

Endpoint Attributes Method Description

/books q: Optional search

term.

genre: Optional

ltering by book genre.

Defaults to “all.”

GET Lists and searches all books. If the q

parameter is present, it’s used as a free-text

search; otherwise, the endpoint can be used

to return lists of books by genre.

/books POST Creates a new book and saves it in the

database

/books/:id GET Returns information about a specic book

/books/:id PUT Updates the information on a book

/books/:id/

authors

GET Returns the author(s) of a specic book

/books/:id/

reviews

GET Returns user reviews for a specic book

/authors genre: Optional;

defaults to “all.”

q: Optional search term

GET Returns a list of authors. If genre is

present, it’s used to lter by the type of book

published. If q is present, it’s used to do a

free- text search on the author’s information.

/authors POST Adds a new author

/authors/:id PUT Updates the data on a specic author

/authors/:id GET Returns the data on a specic author

/authors/:id/

books

GET Returns a list of books written by a specic

author

/stores state: Optional; lters

the list of stores by

state name.

GET Returns the list of stores

/stores POST Adds a new store to the system

/stores/:id GET Returns the data on a specic store

(continued)

CHAPTER 6 PLANNING YOUR REST API

181

Table 6-2. (continued)

Endpoint Attributes Method Description

/stores/:id/

books

q: Optional; does a

full- text search of books

within a specic store.

genre: Optional; lters

the results by genre.

GET Returns a list of books that are in stock at

a specic store. If the attribute q is used, it

performs a full-text search on those books

/stores/:id/

employees

GET Returns a list of the employees working at a

specic store

/stores/:id/

booksales

GET Returns a list of the sales at a specic store

/stores/:id PUT Updates the information about a specic

store

/employees GET Returns a full list of the employees working

across all stores

/employees POST Adds a new employee to the system

/

employees/:id

GET Returns the data on a specic employee

/

employees/:id

PUT Updates the data on a specic employee

/clients GET Lists clients ordered alphabetically by name

/clients POST Adds a new client to the system

/clients/:id GET Returns the data on a specic client

/clients/:id PUT Updates the data on a specic client

(continued)

CHAPTER 6 PLANNING YOUR REST API

182

Tip Even though they’re not specified, all endpoints that deal with listing

resources will accept the following attributes: page (starting at 0, the page number

to return); perpage (the number of items per page to return); and a special

attribute called sort, which contains the field name by which to sort the results

and the order in the following format: [FIELD_NAME]_[ASC|DESC] (e.g., title_asc).

Table6-2 gives us a pretty good idea of the size of the project; with it we’re able to

estimate the amount of work that we have ahead of us.

There is one more aspect to discuss because it isn’t covered in the resources in

Table6-1 or with the endpoints/authentication in Table6-2.

The authentication scheme will be simple. As discussed in Chapter 2, we’ll use the

stateless alternative by signing every request with a MAC (message authentication code).

The server will re-create that code to verify that the request is actually valid. This means

there will not be a signing process embedded into our system; that can be done by the

client. No need to worry about that for now.

Table 6-2. (continued)

Endpoint Attributes Method Description

/booksales start_date: Filters

records that were

created after this date.

end_date: Optional;

lters records that

were created before

this date.

store_id: Optional;

lters records by store.

GET Returns a list of sales. The results can be

ltered by time range or by store.

/booksales POST Records a new book sale

/clientreviews POST Saves a new client review of a book

CHAPTER 6 PLANNING YOUR REST API

183

Note Since it’s not part of the scope of this book, the API will not handle charging

for the book sales. This means that we’ll assume that the book sale was done

outside of our system, and that another system will post the results into our API

to keep a record of it. In a production system, this is a good way to handle this

functionality inside the API itself, thus providing a complete solution.

Keeping Track ofStock per Store

Table6-1 shows that every book tracks the stores at which it is being sold. It is not completely

clear, however, what happens if there is more than one copy of the same book per store.

To keep track of this number, let’s enhance the relation between the books and the

stores models by assigning another element: the number of copies. You’ll see this in a bit

in the UML diagram, but this is how the system will keep global stock of every book.

UML Diagram

With the level of specification we have so far, we could very well skip this step and jump

right into the next one; but for the sake of completeness and getting a clear idea across,

let’s create a basic UML diagram to provide another way to show how all of the resources

of the API will relate to each other.

As you can see in Figure6-3, most of the diagram consists of groups of aggregations

between different resources. The store has a group for employees, a group for books, a

group for the books’ authors (usually it’s one author per book, but there are books that

are co-authored by two or more authors), and a group for client reviews.

CHAPTER 6 PLANNING YOUR REST API

184

Figure 6-3. UML diagram showing the relations between all resources

CHAPTER 6 PLANNING YOUR REST API

185

Choosing aDatabase Storage System

It’s time to stop writing lists of endpoints and creating diagrams; you need to start

picking technologies. In this case, I’ll go over some of the most common choices for a

database storage system. I’ll talk a bit about each one and we’ll decide on one of them.

The bottom line is that all the solutions are valid—you could very well go with any

of them, but we’ll need to choose one in the end, so let’s define what it is needed in the

database system:

• Speed of development: Because you want the process to go quickly

and not have interaction with the database be a bottleneck, you need

something that integrates easily.

• Easy-to-change schema: With everything predened, you have a

pretty solid idea of what the schema is going to look like, but you

might want to adjust things during development. It’s always better if

the storage you’re using allows for this without a lot of hustle.

• Ability to handle entity relations: is means that key/value stores are

out of the question.

• Seamless integration between the entities’ code and the database

representation of the data.

That’s pretty much about it. In this case, we want something that can be integrated

fast, changed easily, and is not key/value.

Therefore, the options are as follows:

• MySQL

1

: A classic choice when it comes to relational databases.

• PostgreSQL

2

: Another great choice when it comes to relational

database engines.

• MongoDB

3

: A document-based NoSQL database engine.

So, now that you have our list of options, let’s analyze how well each one of them

complies with our requirements.

1

See http://mysql.com/.

2

See http://www.postgresql.org/.

3

See http://www.mongodb.org/.

CHAPTER 6 PLANNING YOUR REST API

186

Fast Integration

Integration with the system means how easily the modules interact with the specific

database engine. With MySQL and PostgreSQL, there is Sequelize,

4

which provides very

complete and powerful object-relational mapping (ORM). It lets you focus more on the

data model than on the actual engine particularities. Besides, if you use it right, you can

potentially switch between both engines with minimum impact on the code.

On the other hand, with MongoDB you have Mongoose.js,

5

which allows you to

abstract your code from the engine, simplifying your task when it comes to defining the

schemas, validations, and so forth.

Easy-to-Change Schemas

This time around, the fixed structure provided by both MySQL and PostgreSQL makes it

harder to maintain dynamic schemas, so every time you make a change, you’ll need to

update the schema by running migrations.

The lack of structure provided by the NoSQL engines makes MongoDB the perfect

choice for our project, because making a change on the schema is as simple as making

the changes on the definition code—no migration or anything else required.

Ability toHandle Entity Relations

Since we’re leaving out key/value stores like Redis,

6

all of our three options are able to

handle entity relations. Both MySQL and PostgreSQL are especially good at this, since

they’re both relational database engines. But let’s not rule out MongoDB; it is document-

based NoSQL storage, which in turn allows you to have documents (that translate

directly into a MySQL record) and subdocuments, which are a special kind of relation

that we don’t have with our relational options.

Subdocument relations help to simplify both schemas and queries when working

with the data. You saw in Figure6-3 that most of our relations are based on aggregation,

so this might be a good way to solve that.

4

See http://sequelizejs.com/.

5

See http://mongoosejs.com/.

6

See http://redis.io.

CHAPTER 6 PLANNING YOUR REST API

187

Seamless Integration Between Our Models andtheDatabase Entities

This is more of a comparison between Sequelize and Mongoose. Since they both abstract

the storage layer, you need compare how that abstraction affects this point.

Ideally, we want our entities (our resources’ representations in the code) to be

passed to our storage layer or to interact with the storage layer. We don’t want to require

an extra type of object, usually called a DTO (data transfer object), to transfer the state of

our entities between layers.

Luckily, the entities provided by Sequelize and by Mongoose fall into this category,

so we might as well call it a draw.

And theWinner Is…

We need to pick one, so let’s summarize:

• Fast integration: Let’s give this one to Sequelize, since it comes with

the added bonus of being able to switch engines with minimum

impact.

• Easy-to-change schemas: MongoDB wins this one, hands down.

• Handling of entity relations: I’d like to give this one to MongoDB as

well, mainly due to the subdocuments feature.

• Seamless integration with our data models: This one is a draw, so

we’re not counting it.

The final result seems to point toward MongoDB, but it’s a pretty close win, so in

the end, personal experience needs to be taken into account as well. Personally, I find

MongoDB to be a very interesting alternative when prototyping and creating something

new, something that might change during the development process many times, but this

is why we’ll go with it for our development. This way there is the extra insurance that if

we need to change something, like adapting our data model to a new structure, we can

do so easily and with minor impact.

The obvious module choice here is Mongoose, which provides a layer of abstraction

over the MongoDB driver.

CHAPTER 6 PLANNING YOUR REST API

188

Choosing theRight Modules fortheJob

This is the last step of our preparation process. Now that you know the problem to solve

and you have a pretty well-defined specification of how to handle the development, the

only thing left to do, aside from actually coding, is to pick the right modules.

In Chapter 5, I went over a list of modules that would help us achieve a pretty

complete RESTful system; so let’s quickly pick some of them for this development:

• Restify will be the basis of everything we do. It’ll provide the structure

needed to handle and process the requests and to provide a response

to them.

• Swagger will be used to create the documentation. In Chapter 5,

I talked about swagger-node-express, but just like that, there is one

that works with Restify called (unsurprisingly enough) swagger-

node- restify.

7

is module was chosen because it integrates into

our project, allowing us to autogenerate our documentation based

on our original code, instead of having to maintain two dierent

repositories.

• Halson will be our module of choice for adding hypermedia to our

responses. Mainly chosen because it appears to be more mature than

HAL (the other modules examined for this task).

• Finally, the validation of our JSONs will be done using TV4, mainly

because it allows us to gather all validation errors at once.

Note These are not the only modules that we’ll use; there are other minor

auxiliary modules that will help us in different situations, but the ones listed are the

ones that will help us achieve a RESTful API.

7

See https://www.npmjs.com/package/swagger-node-restify.

CHAPTER 6 PLANNING YOUR REST API

189

Summary

We now have all we need to start coding. We know the extent of the API for the bookstore

chain that we’ll develop. We have planned the internal architecture of the system and

have chosen the main modules that we’ll use.

In the next chapter, we’ll start coding our API.By the end of the chapter, we should

have a full-fledged working bookstore API.

CHAPTER 6 PLANNING YOUR REST API

191

F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1_7

CHAPTER 7

Developing Your

REST API

Now that we have finally defined the tools that we’ll use and the project that we’ll

develop with them, we’re ready to actually start coding. This chapter will cover that

part—from the organization of the files (the directory structure), through the small

design decisions made during development, and finally the code itself.

This chapter will display the entire source code for the project, but we’ll only go

over the relevant parts. Sadly, some bits and pieces are just plain boring (like the JSON

Schema definitions and the simpler models), so I’ll skip it. These things should be pretty

self-explanatory to developers anyway, no matter the level of expertise.

I’ll cover the development stage as follows:

• Minor simplifications/design decisions made during development

• Folder structure, because it’s always important to understand where

everything is and why

• e code itself, le by le, including explanation when needed

Note The code in this chapter is but one of the infinitely potential ways of solving

the problem presented in Chapter 6. It attempts to show the concepts and modules

mentioned throughout this book. It’s also meant to show you only one potential

development process, which tries to be agile and dynamic at the same time.

Of course, there are different ways to go about the process, which may be better or

worse for every reader.

192

Minor Changes tothePlan

We spent two whole chapters going over different modules and planning the entire

process to develop the API.We made some diagrams, and we even listed every resource

and endpoint that we would need.

And yet, during development, the plan changes—not by a lot, but we still need to

fine-tune some aspects of the design.

This isn’t necessarily a bad thing, though. If the original plan changes significantly,

then yes, that would mean we definitely did something wrong in the planning; but there

is no escape from minor changes at this stage, unless you spend a lot more time in your

design phase. I’m talking about going the whole nine yards here: writing detailed use

cases with their corresponding edge conditions, flow charts—the works. That process,

when done right and when followed by the team implementing the solution, most likely

results in no changes during development. But for that to happen, we need a lot more

time, and let’s face it, aside from being the boring part of development (disclaimer: if

you actually like that part better than developing, there’s nothing wrong with you; I just

haven’t ever met anyone like you), it’s not this book’s focus either.

So we can play with the design, use the partial analysis and planning that we did in

the previous chapter, and live with the consequences, which are very little, as you’ll see.

Simplification oftheStore–Employee Relationship

When I listed every resource, I said that the store would keep a list of employees and

that each employee would keep a direct reference to the store. To maintain those

relationships in MongoDB, however, means extra work. And since we don’t really need

this, we’ll just keep the employees’ records unaware of their assigned store and make

sure that each store keeps up with the employees working in it.

Adding Swagger UI

I talked about Swagger back in Chapter 5, and I briefly mentioned Swagger UI, but

I never really explained a lot. The Swagger UI project is the UI we’ll use to test our

API.The swagger-node-express and swagger-node-restify modules provide the back-end

infrastructure that the UI needs; but without the Swagger UI project, we have nothing.

CHAPTER 7 DEVELOPING YOUR REST API

193

So, just download version 2.1.5 of this project from https://github.com/swagger-

api/swagger-ui/tree/v2.1.5 and add its dist folder into your project’s root. I’ll go over

how to configure it in a bit.

Simplified Security

To simplify the security, we’ll work under the premise that we’re not really making a

public API but rather an API for clients that are directly under our control.

That means that we will not require every client to request an access token with a

limited life span. Instead, we’ll work under the assumption that when we set up a new

client on a new branch, we share the secret passphrase, so the clients will always send

the MAC code encrypted using this passphrase, and the API will re-hash each request to

make sure both results match. This way we’re still validating the requests and we’ll still

remain true to REST, because this method is stateless. We’re just simplifying the addition

of new client applications.

To explain a bit further, each client will send, on every request, two very specific

pieces of information:

• A special header called hmacdata with the information being

encrypted

• The api_key parameter with the value of the encryption result

Upon receiving the request, the API will grab the data from the header and encrypt

it again using the correct passphrase. If the result is the same as the value of the api_key

parameter, then it’ll dim the request as authentic. Otherwise, it’ll reject the request with

a 401 error code.

A Small Backdoor forSwagger

The other change that we’re making is because the Swagger UI has no de facto support

for our authentication scheme. We can send a fixed api_key parameter, but we would

have to change the code of the client to get it to use the same algorithm we’re using.

This is why we’ve added a small backdoor in our code, to let the Swagger -UI go by

without needing to authenticate each request.

The hack is very simple. Since the UI can send a fixed api_key, then we’ll let all

requests that have an api_key equal to 777 pass, automatically trusting them.

CHAPTER 7 DEVELOPING YOUR REST API

194

This backdoor will need to be removed when going into production to avoid any

security issues, of course.

Once this has been added, you can visit http://localhost:9000/swagger-ui to

check out the UI.

MVC

In Chapter 4, I went over several variations of the MVC pattern, but never actually settled

on one to be used on our API.Personally, I really liked the idea behind Hierarchical

MVC, since it allows for some really clean code.

That said, it also means extra work when developing, and considering that there

aren’t many cases where in one controller we’re dealing with resources from another,

we’ll just try to keep it simple and go with a basic MVC.

This means that we’ll have the following key elements in our project:

• Controllers: Handles requests and calls upon the models for further

action

• Models: Holds the main logic of the API.Since in our simple case that

logic is basically querying the database, these will be the models used

by Mongoose. is will simplify our architecture. Also, Mongoose

provides dierent mechanisms to add extra behaviors to our models

(things like setting instance methods or post-action hooks).

• View: e view will be embedded inside the model’s code in the

form of a method that translates the specics of one model into a

HAL + JSON that can be returned back to the client.

Folder Structure

To completely understand the design behind our API, let’s quickly take a look at the

folder structure that I’ve set up (see Figure7-1).

CHAPTER 7 DEVELOPING YOUR REST API

195

Here are the folders we’ll be creating and using:

• controllers: This folder contains the code for our controllers. It also

has an index.js file to handle exporting the contents of the required

controller files. There is also a base controller here, which contains

all the generic methods that all controllers should have; so every new

controller can extend this and inherit said methods.

• lib: is folder contains the miscellaneous code not big enough to

have its own folder but required across several dierent places in our

project; for instance, database access, helper functions, and so forth.

• models: Inside this folder are the model les. Normally when working

with Mongoose, a model’s le has the schema denition, and you

return the instantiation of that schema as your model. In our case,

the actual denition is somewhere else, so this code handles loading

that external denition, adding the extra behavior specic to each

model, and then returning it.

Figure 7-1. Project folder structure

CHAPTER 7 DEVELOPING YOUR REST API

196

• request_schemas: Inside this folder are the JSON Schemas used to

validate the dierent requests.

• schemas: ese are the JSON Schemas of the models, used for the

Swagger module to dene the UI for testing and for the Mongoose

model’s denition. We will have to add some code to translate from

the rst one to the latter, since they don’t use the same format.

• swagger-ui: is folder contains the contents of the Swagger UI

project. We’ll need to do some minor adjustments to the index.html

le to make it work as we expect it.

• node_modules: is folder will be created automatically by npm, and

it’ll contain the modules listed on you package.json le. You don’t

really have to worry about maintaining (or even creating) this folder,

it’ll appear there once you run npm install for the rst time.

• conﬁg: e conﬁg folder is used by the conﬁg module, which will

look inside it by default. Your conguration should be inside a JSON

le called default.json. Any environment-specic conguration

will be added by creating conguration les aptly named (such

as production.json, or development.json, which you can later

reference using the NODE_ENV environment variable

1

).

The Source Code

Here I’ll list the entire code for the project, including some basic description of the code

if required. I’ll go folder by folder, following the order shown in Figure7-1.

The default configuration values are stored in this file (Listing 7-1). This JSON

contains values later used throughout the code, as you’ll see. You could simply require

the file, and directly access those values, but by accessing them through the config

modue, you’ll get the right behavior when dealing with multiple environment-specific

configurations.

1

See the official documentation for more details https://www.npmjs.com/package/config

CHAPTER 7 DEVELOPING YOUR REST API

197

config

Listing 7-1. config/default.json

{

"secretKey": "this is a secret key, right here",

"env": "Default",

"server": {

"name": "ComeNRead API",

"version": "2.0.0",

"port": 9000

},

"database": {

"host": "mongodb://localhost",

"dbname": "comenread"

}

Controllers

This file (Listing 7-2) is used to export each controller. Using this technique, we can

import the entire folder like if it was a module, like this:

Listing 7-2. /controllers/index.js

module.exports = {

BookSales: require("./booksales"),

Stores: require("./stores"),

Employees: require("./employees"),

ClientReviews: require("./clientreviews"),

Clients: require("./clients"),

Books: require("./books"),

Authors: require("./authors")

}

var controllers = require("/controllers")

CHAPTER 7 DEVELOPING YOUR REST API

198

Listing 7-3. /controllers/basecontroller.js

const restify = require("restify"),

errors = require("restify-errors"),

halson = require("halson"),

logger = require("../lib/logger")

class BaseController {

constructor() {

this.actions = []

this.server = null

}

setUpActions(app ,sw) {

this.server = app

this.actions.forEach(act => {

let method = act['spec']['method']

logger.info(`Setting up auto-doc for (${method} ) -

${act['spec']['nickname']}`)

sw['add' + method](act)

app[method.toLowerCase()](act['spec']['path'],

act['action'])

})

}

addAction(spec, fn) {

let newAct = {

'spec': spec,

action: fn.bind(this)

}

this.actions.push(newAct)

}

RESTError(type, msg) {

logger.error("Error of type" + type + "found:" + msg.

toString());

CHAPTER 7 DEVELOPING YOUR REST API

199

if(errors[type]) {

return new errors[type](msg.toString())

} else {

return {

error: true,

type: type,

msg: msg

}

writeHAL(res, obj) {

if(Array.isArray(obj)) {

let newArr = obj.map( item => {

return item.toHAL();

})

obj = halson(newArr)

} else {

if(obj && obj.toHAL) {

obj = obj.toHAL()

}

if(!obj) {

obj = {}

}

res.json(obj)

}

module.exports = BaseController

Every controller extends this class (Listing 7-3), gaining access to the methods shown

earlier. We’ll use basic prototypical inheritance, as you’ll see in a bit when we start listing

the other controllers’ code.

CHAPTER 7 DEVELOPING YOUR REST API

200

Let’s quickly go over the methods exposed in the code from Listing 7-3.

• setUpActions: This method is called upon instantiation of the

controller; it is meant to add the actual routes to the HTTP server.

This method is called during the initialization sequence for all

controllers exported by the index.js file.

• addAction: is method denes an action, which consists of the

specs for that action and the actual function code. e specs are used

by Swagger to create the documentation, but they’re also used by our

code to set up the route; so there are bits inside the JSON spec that

are also meant for the server, such as the path and method attributes.

• RESTError: is is a simple wrapper method around all the error

methods provided by Restify’s error extension.

2

It provides the benet

of cleaner code.

• writeHAL: Every model dened (as you’ll see soon enough) has a toHAL

method, and the writeHAL methods take care of calling it for every model

we’re trying to render. It basically centralizes the logic that deals with

collections or simple objects, depending on what we’re trying to render.

Listing 7-4. /controllers/books.js

const BaseController = require("./basecontroller"),

swagger = require("swagger-node-restify")

class Books extends BaseController {

constructor(lib) {

super();

this.lib = lib;

}

/**

Helper method for the POST action, it takes two lists of items with

properties calls "store" and "copies" and returns a single list, with

"store" being a unique key

*/

2

See https://github.com/restify/errors.

CHAPTER 7 DEVELOPING YOUR REST API

201

mergeStores(list1, list2) {

let stores1 = {}

let stores2 = {}

let storesMap1 = list1.reduce( (theMap, theItem) => {

if(theItem.store) theMap[theItem.store] = theItem.copies;

return theMap;

}, {})

let storesMap2 = list2.reduce( (theMap, theItem) => {

if(theItem.store) theMap[theItem.store] = theItem.copies;

return theMap;

}, {})

let stores = Object.assign(storesMap1, storesMap2)

return Object.keys().map( (k) => {

return {store: k, copies: stores[k]}

})

}

list(req, res, next) {

let criteria = {}

if(req.params.q) {

let expr = new RegExp('.*' + req.params.q + '.*')

criteria.$or = [

{title: expr},

{isbn_code: expr},

{description: expr}

]

}

if(req.params.genre) {

criteria.genre = req.params.genre

}

CHAPTER 7 DEVELOPING YOUR REST API

202

this.lib.db.model('Book')

.find(criteria)

.populate('stores.store')

.exec((err, books) => {

if(err) return next(err)

this.writeHAL(res, books)

})

}

details(req, res, next) {

let id = req.params.id

if(id) {

this.lib.db.model("Book")

.findOne({_id: id})

.populate('authors')

.populate('stores')

.populate('reviews')

.exec((err, book) => {

if(err) return next(this.RESTError('InternalServerError', err))

if(!book) {

return next(this.RESTError('ResourceNotFoundError', 'Book not

found'))

}

this.writeHAL(res, book)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Missing book id'))

}

create(req, res, next) {

let bookData = req.body

if(bookData) {

let isbn = bookData.isbn_code

this.lib.db.model("Book")

.findOne({isbn_code: isbn})

.exec((err, bookModel) => {

CHAPTER 7 DEVELOPING YOUR REST API

203

if(!bookModel) {

bookModel = this.lib.db.model("Book")(bookData)

} else {

bookModel.stores = this.mergeStores(bookModel.stores, bookData.

stores)

}

bookModel.save((err, book) => {

if(err) return next(this.RESTError('InternalServerError',

err))

this.writeHAL(res, book)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Missing content of

book'))

}

bookAuthors(req, res, next) {

let id = req.params.id

if(id) {

this.lib.db.model("Book")

.findOne({_id: id})

.populate('authors')

.exec((err, book) => {

if(err) return next(this.RESTError('InternalServerError', err))

if(!book) {

return next(this.RESTError('ResourceNotFoundError', 'Book not

found'))

}

thihs.writeHAL(res, book.authors)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Missing book id'))

}

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bookReviews(req, res,next) {

let id = req.params.id

if(id) {

this.lib.db.model("Book")

.findOne({_id: id})

.populate('reviews')

.exec((err, book) => {

if(err) return next(this.RESTError('InternalServerError', err))

if(!book) {

return next(this.RESTError('ResourceNotFoundError', 'Book not

found'))

}

this.writeHAL(res, book.reviews)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Missing book id'))

}

update(req, res, next) {

let data = req.body

let id = req.params.id

if(id) {

this.lib.db.model("Book").findOne({_id: id}).exec((err, book) => {

if(err) return next(this.RESTError('InternalServerError', err))

if(!book) return next(this.RESTError('ResourceNotFoundError', 'Book

not found'))

book = Object.assign(book, data)

book.save((err, data) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, data.toJSON())

})

} else {

next(this.RESTError('InvalidArgumentError', 'Invalid id received'))

}

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205

}

module.exports = function(lib) {

let controller = new Books(lib);

controller.addAction({

'path': '/books',

'method': 'GET',

'summary': 'Returns the list of books',

"params": [ swagger.queryParam('q', 'Search term', 'string'),

swagger.queryParam('genre','Filter by genre', 'string')],

'responseClass': 'Book',

'nickname': 'getBooks'

}, controller.list)

controller.addAction({

'path': '/books/{id}',

'method': 'GET',

'params': [ swagger.pathParam('id', 'The Id of the book','int') ],

'summary': 'Returns the full data of a book',

'responseClass': 'Book',

'nickname': 'getBook'

}, controller.details )

controller.addAction({

'path': '/books',

'method': 'POST',

'params': [ swagger.bodyParam('book', 'JSON representation of the

new book','string') ],

'summary': 'Adds a new book into the collectoin',

'responseClass': 'Book',

'nickname': 'newBook'

}, controller.create)

controller.addAction({

'path': '/books/{id}/authors',

'method': 'GET',

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206

'params': [ swagger.pathParam('id', 'The Id of the book','int') ],

'summary': 'Returns the list of authors of one specific book',

'responseClass': 'Author',

'nickname': 'getBooksAuthors'

}, controller.bookAuthors)

controller.addAction({

'path': '/books/{id}/reviews',

'method': 'GET',

'params': [ swagger.pathParam('id', 'The Id of the book','int') ],

'summary': 'Returns the list of reviews of one specific book',

'responseClass': 'BookReview',

'nickname': 'getBooksReviews'

}, controller.bookReviews)

controller.addAction({

'path': '/books/{id}',

'method': 'PUT',

'params': [ swagger.pathParam('id', 'The Id of the book to

update','string'),

swagger.bodyParam('book', 'The data to change on the

book', 'string') ],

'summary': 'Updates the information of one specific book',

'responseClass': 'Book',

'nickname': 'updateBook'

}, controller.update)

return controller

}

The code for this controller (Listing 7-4) is very straightforward; in it we see the

basic mechanics we’ve defined for this particular project, on how to declare a controller

and its actions. We also have the special case for the POST action, which takes care of

checking for the ISBN of the new book to see if it is trying to add it in stock at another

store. If the ISBN already exists, then the book is merged to all the relevant stores

(method mergeStores); otherwise, it’ll just create the new record.

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207

For every controller, we’re creating a new class that inherits from the

BaseController, which gives us the ability to add custom behavior if we wanted to and

also to remove the common code (such as the setUpActions and RESTError methods)

and move it into a single place.

The controller files are required during initialization of the API and then used on

the setUpRoutes function inside the helpers.js file. And when that happens, the lib

object is passed to them:

function setupRoutes(server, swagger, lib) {

for(controller in lib.controllers) {

cont = lib.controllers[controller](lib)

cont.setUpActions(server, swagger)

}

This in turn, means that the lib object is received by the export function, which is

the one in charge of instantiating the new controller and setting up its actions as part of

swagger’s documentation to finally return it back to the requiring code.

Here are some other interesting bits from Listing 7-4:

• The getBooks action shows how to do simple regular expression–

based filtering with Mongoose.

• e update action is not actually using the update method from

Mongoose but instead loads the model using the extend method

from the underscore, and nally calls the save method on the model.

is is done for one simple reason: the update method doesn’t trigger

any post-hooks on the models, but the save method does, so if we

wanted to add behavior to react to an update on the model, this

would be the way to go about it.

Listing 7-5. /controllers/stores.js

const BaseController = require("./basecontroller"),

swagger = require("swagger-node-restify")

class Stores extends BaseController {

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208

constructor(lib) {

super();

this.lib = lib;

}

list(req, res, next) {

let criteria = {}

if(req.params.state) {

criteria.state = new RegExp(req.params.state,'i')

}

this.lib.db.model('Store')

.find(criteria)

.exec((err, list) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, list)

})

}

details(req, res, next) {

let id = req.params.id

if(id) {

this.lib.db.model('Store')

.findOne({_id: id})

.populate('employees')

.exec((err, data) => {

if(err) return next(this.RESTError('InternalServerError', err))

if(!data) return next(this.RESTError('ResourceNotFoundError',

'Store not found'))

this.writeHAL(res, data)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Invalid id'))

}

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209

storeBooks(req, res, next) {

let id = req.params.id

if(id) {

let criteria = {stores: {$elemMatch: {"store": id}}}

if(req.params.q) {

let expr = new RegExp('.*' + req.params.q + '.*', 'i')

criteria.$or = [

{title: expr},

{isbn_code: expr},

{description: expr}

]

}

if(req.params.genre) {

criteria.genre = req.params.genre

}

//even though this is the stores controller, we deal directly with

books here

this.lib.db.model('Book')

.find(criteria)

.populate('authors')

.exec((err, data) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, data)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Invalid id'))

}

storeEmployees(req, res, next) {

let id = req.params.id

if(id) {

this.lib.db.model('Store')

.findOne({_id: id})

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210

.populate('employees')

.exec((err, data) => {

if(err) return next(this.RESTError('InternalServerError', err))

if(!data) {

return next(this.RESTError('ResourceNotFoundError', 'Store not

found'))

}

console.log(data)

this.writeHAL(res, data.employees)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Invalid id'))

}

storeBooksales(req, res, next) {

let id = req.params.id

if(id) {

//even though this is the stores controller, we deal directly with

booksales here

this.lib.db.model('Booksale')

.find({store: id})

.populate('client')

.populate('employee')

.populate('books')

.exec((err, data) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, data)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Invalid id'))

}

create(req, res, next) {

let data = req.body

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211

if(data) {

let newStore = this.lib.db.model('Store')(data)

newStore.save((err, store) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, store)

})

} else {

next(this.RESTError('InvalidArgumentError', 'No data received'))

}

update(req, res, next) {

let data = req.body

let id = req.params.id

if(id) {

this.lib.db.model("Store").findOne({_id: id}).exec((err, store) => {

if(err) return next(this.RESTError('InternalServerError', err))

if(!store) return next(this.RESTError('ResourceNotFoundError',

'Store not found'))

store = Object.assign(store, data)

store.save((err, data) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, data);

})

} else {

next(this.RESTError('InvalidArgumentError', 'Invalid id received'))

}

module.exports = lib => {

let controller = new Stores(lib);

controller.addAction({

'path': '/stores',

'method': 'GET',

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212

'summary': 'Returns the list of stores ',

'params': [swagger.queryParam('state', 'Filter the list of stores by

state', 'string')],

'responseClass': 'Store',

'nickname': 'getStores'

}, controller.list);

controller.addAction({

'path': '/stores/{id}',

'method': 'GET',

'params': [swagger.pathParam('id','The id of the

store','string')],

'summary': 'Returns the data of a store',

'responseClass': 'Store',

'nickname': 'getStore'

}, controller.details )

controller.addAction({

'path': '/stores/{id}/books',

'method': 'GET',

'params': [swagger.pathParam('id','The id of the store','string'),

swagger.queryParam('q', 'Search parameter for the books',

'string'),

swagger.queryParam('genre', 'Filter results by genre',

'string')],

'summary': 'Returns the list of books of a store',

'responseClass': 'Book',

'nickname': 'getStoresBooks'

}, controller.storeBooks)

controller.addAction({

'path': '/stores/{id}/employees',

'method': 'GET',

'params': [swagger.pathParam('id','The id of the

store','string')],

'summary': 'Returns the list of employees working on a store',

'responseClass': 'Employee',

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213

'nickname': 'getStoresEmployees'

}, controller.storeEmployees)

controller.addAction({

'path': '/stores/{id}/booksales',

'method': 'GET',

'params': [swagger.pathParam('id','The id of the store','string')],

'summary': 'Returns the list of booksales done on a store',

'responseClass': 'BookSale',

'nickname': 'getStoresBookSales'

}, controller.storeBooksales)

controller.addAction({

'path': '/stores',

'method': 'POST',

'summary': 'Adds a new store to the list',

'params': [swagger.bodyParam('store', 'The JSON data of the store',

'string')],

'responseClass': 'Store',

'nickname': 'newStore'

}, controller.create)

controller.addAction({

'path': '/stores/{id}',

'method': 'PUT',

'summary': "UPDATES a store's information",

'params': [swagger.pathParam('id','The id of the

store','string'), swagger.bodyParam('store', 'The new

information to update', 'string')],

'responseClass': 'Store',

'nickname': 'updateStore'

}, controller.update)

return controller

}

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214

The code from Listing 7-5 is very similar to that of the Books controller. It does,

however, have something of notice: the getStoresBookSales action clearly shows what

happens when we don’t use a Hierarchical MVC model. I said that this is not a common

case, so it would be fine for the purpose of this book, but it clearly shows how separation

of concerns is broken in the strictest of senses, by acting over the model of another

controller instead of going through that other controller. Given the added complexity

that mechanism would imply to our code, we’re better off looking the other way for the

time being.

Listings 7-6 to 7-10 show the code of the three remaining controllers. They don’t

particularly show anything new compared to the previous ones, so we’ll just look at their

code and the occasional code comment.

Listing 7-6. /controllers/authors.js

const BaseController = require("./basecontroller"),

swagger = require("swagger-node-restify")

class BookSales extends BaseController {

constructor(lib) {

super();

this.lib = lib;

}

queryAuthors(res, next, criteria, bookIds) {

if(bookIds) {

criteria.books = {$in: bookIds}

}

this.lib.db.model('Author')

.find(criteria)

.exec((err, authors) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, authors)

})

}

CHAPTER 7 DEVELOPING YOUR REST API

215

list(req, res, next) {

let criteria = {}

if(req.params.q) {

let expr = new RegExp('.*' + req.params.q + '.*', 'i')

criteria.$or = [

{name: expr},

{description: expr}

]

}

let filterByGenre = false || req.params.genre

if(filterByGenre) {

this.lib.logger.debug("Filtering by genre:" + filterByGenre)

this.lib.db.model('Book')

.find({genre: filterByGenre})

.exec((err, books) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.queryAuthors(res, next, criteria, _.pluck(books, '_id'))

})

} else {

this.queryAuthors(res, next, criteria)

}

details(req, res, next) {

let id = req.params.id

if(id) {

this.lib.db.model('Author')

.findOne({_id: id})

.exec((err, author) => {

if(err) return next(this.RESTError('InternalServerError', err))

if(!author) {

return next(this.RESTError('ResourceNotFoundError', 'Author not

found'))

}

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216

this.writeHAL(res, author)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Missing author id'))

}

create(req, res, next) {

let body = req.body

if(body) {

let newAuthor = this.lib.db.model('Author')(body)

newAuthor.save((err, author) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, author)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Missing author id'))

}

update(req, res, next) {

let data = req.body

let id = req.params.id

if(id) {

this.lib.db.model("Author").findOne({_id: id}).exec((err, author) =>

{

if(err) return next(this.RESTError('InternalServerError', err))

if(!author) return next(this.RESTError('ResourceNotFoundError',

'Author not found'))

author = Object.assign(author, data)

author.save((err, data) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, data)

})

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217

} else {

next(this.RESTError('InvalidArgumentError', 'Invalid id received'))

}

authorBooks(req, res, next) {

let id = req.params.id

if(id) {

this.lib.db.model('Author')

.findOne({_id: id})

.populate('books')

.exec((err, author) => {

if(err) return next(this.RESTError('InternalServerError', err))

if(!author) {

return next(this.RESTError('ResourceNotFoundError', 'Author not

found'))

}

this.writeHAL(res, author.books)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Missing author id'))

}

module.exports = function(lib) {

let controller = new BookSales(lib)

//list

controller.addAction({

'path': '/authors',

'method': 'GET',

'summary' :'Returns the list of authors across all stores',

'params': [ swagger.queryParam('genre', 'Filter authors by genre

of their books', 'string'),

CHAPTER 7 DEVELOPING YOUR REST API

218

swagger.queryParam('q', 'Search

parameter', 'string')],

'responseClass': 'Author',

'nickname': 'getAuthors'

}, controller.list)

//get

controller.addAction({

'path': '/authors/{id}',

'summary': 'Returns all the data from one specific author',

'method': 'GET',

'params': [swagger.pathParam('id','The id of the author','string')],

'responseClass': 'Author',

'nickname': 'getAuthor'

}, controller.details )

//post

controller.addAction({

'path': '/authors',

'summary': 'Adds a new author to the database',

'method': 'POST',

'params': [swagger.bodyParam('author', 'JSON representation of

the data', 'string')],

'responseClass': 'Author',

'nickname': 'addAuthor'

}, controller.create )

//put

controller.addAction({

'path': '/authors/{id}',

'method': 'PUT',

'summary': "UPDATES an author's information",

'params': [swagger.pathParam('id','The id of the author','string'),

swagger.bodyParam('author', 'The new

information to update', 'string')],

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219

'responseClass': 'Author',

'nickname': 'updateAuthor'

}, controller.update)

// /books

controller.addAction({

'path': '/authors/{id}/books',

'summary': 'Returns the data from all the books of one specific

author',

'method': 'GET',

'params': [ swagger.pathParam('id', 'The id of the author',

'string')],

'responseClass': 'Book',

'nickname': 'getAuthorsBooks'

}, controller.authorBooks )

return controller

}

Listing 7-7. /controllers/booksales.js

const BaseController = require("./basecontroller"),

swagger = require("swagger-node-restify")

class BookSales extends BaseController {

constructor(lib) {

super();

this.lib = lib;

}

list(req, res, next) {

let criteria = {}

if(req.params.start_date)

criteria.date = {$gte: req.params.start_date}

if(req.params.end_date)

criteria.date = {$lte: req.params.end_date}

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220

if(req.params.store_id)

criteria.store = req.params.store_id

this.lib.db.model("Booksale")

.find(criteria)

.populate('books')

.populate('client')

.populate('employee')

.populate('store')

.exec((err, sales) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, sales)

})

}

create(req, res, next) {

let body = req.body

if(body) {

let newSale = this.lib.db.model("Booksale")(body)

newSale.save((err, sale) => {

if(err) return next(ths.RESTError('InternalServerError', err))

this.writeHAL(res, sale)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Missing json data'))

}

module.exports = function(lib) {

let controller = new BookSales(lib);

controller.addAction({

'path': '/booksales',

'method': 'GET',

'summary': 'Returns the list of book sales',

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221

'params': [ swagger.queryParam('start_date', 'Filter sales done

after (or on) this date', 'string'),

swagger.queryParam('end_date', 'Filter sales done on or

before this date', 'string'),

swagger.queryParam('store_id', 'Filter sales done on

this store', 'string')

],

'responseClass': 'BookSale',

'nickname': 'getBookSales'

}, controller.list)

controller.addAction({

'path': '/booksales',

'method': 'POST',

'params': [ swagger.bodyParam('booksale', 'JSON representation of

the new booksale','string') ],

'summary': 'Records a new booksale',

'responseClass': 'BookSale',

'nickname': 'newBookSale'

}, controller.create)

return controller

}

Listing 7-8. /controllers/clientreviews.js

const BaseController = require("./basecontroller"),

swagger = require("swagger-node-restify")

class ClientReviews extends BaseController {

constructor(lib) {

super();

this.lib = lib;

}

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222

create(req, res, next) {

let body = req.body

if(body) {

let newReview = this.lib.db.model('ClientReview')(body)

newReview.save((err, rev) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, rev)

})

}

module.exports = function(lib) {

let controller = new ClientReviews(lib);

controller.addAction({

'path': '/clientreviews',

'method': 'POST',

'summary': 'Adds a new client review to a book',

'params': [swagger.bodyParam('review', 'The JSON representation

of the review', 'string')],

'responseClass': 'ClientReview',

'nickname': 'addClientReview'

}, controller.create)

return controller

}

Listing 7-9. /controllers/clients.js

const BaseController = require("./basecontroller"),

swagger = require("swagger-node-restify")

class Clients extends BaseController {

constructor(lib) {

super();

this.lib = lib;

}

CHAPTER 7 DEVELOPING YOUR REST API

223

list(req, res, next) {

this.lib.db.model('Client').find().sort('name').exec((err, clients) =>

{

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, clients)

})

}

create(req, res, next) {

let newClient = req.body

let newClientModel = this.lib.db.model('Client')(newClient)

newClientModel.save((err, client) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, client)

})

}

details(req, res, next) {

let id = req.params.id

if(id != null) {

this.lib.db.model('Client').findOne({_id: id}).exec((err, client) =>

{

if(err) return next(this.RESTError('InternalServerError',err))

if(!client) return next(this.RESTError('ResourceNotFoundError',

'The client id cannot be found'))

this.writeHAL(res, client)

})

} else {

next(this.RESTError('InvalidArgumentError','Invalid client id'))

}

update(req, res, next) {

let id = req.params.id

if(!id) {

return next(this.RESTError('InvalidArgumentError','Invalid id'))

} else {

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224

let model = this.lib.db.model('Client')

model.findOne({_id: id})

.exec((err, client) => {

if(err) return next(this.RESTError('InternalServerError', err))

client = Object.assign(client, req.body)

client.save((err, newClient) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, newClient)

})

}

module.exports = (lib) => {

let controller = new Clients(lib);

controller.addAction({

'path': '/clients',

'method': 'GET',

'summary': 'Returns the list of clients ordered by name',

'responseClass':'Client',

'nickname': 'getClients'

}, controller.list )

controller.addAction({

'path': '/clients',

'method': 'POST',

'params': [swagger.bodyParam('client', 'The JSON representation

of the client', 'string')],

'summary': 'Adds a new client to the database',

'responseClass': 'Client',

'nickname': 'addClient'

}, controller.create )

controller.addAction({

'path': '/clients/{id}',

'method': 'GET',

CHAPTER 7 DEVELOPING YOUR REST API

225

'params': [swagger.pathParam('id', 'The id of the client',

'string')],

'summary': 'Returns the data of one client',

'responseClass': 'Client',

'nickname': 'getClient'

}, controller.details)

controller.addAction({

'path': '/clients/{id}',

'method': 'PUT',

'params': [swagger.pathParam('id', 'The id of the client',

'string'), swagger.bodyParam('client', 'The content to

overwrite', 'string')],

'summary': 'Updates the data of one client',

'responseClass': 'Client',

'nickname': 'updateClient'

}, controller.update )

return controller

}

Listing 7-10. /controllers/employees.js

const BaseController = require("./basecontroller"),

swagger = require("swagger-node-restify")

class Employees extends BaseController {

constructor(lib) {

super();

this.lib = lib;

}

list(req, res, next) {

this.lib.db.model('Employee').find().exec((err, list) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, list)

})

}

CHAPTER 7 DEVELOPING YOUR REST API

226

details(req, res, next) {

let id = req.params.id

if(id) {

this.lib.db.model('Employee').findOne({_id: id}).exec((err, empl) => {

if(err) return next(err)

if(!empl) {

return next(this.RESTError('ResourceNotFoundError', 'Not found'))

}

this.writeHAL(res, empl)

})

} else {

next(this.RESTError('InvalidArgumentError', 'Invalid id'))

}

create(req, res, next) {

let data = req.body

if(data) {

let newEmployee = this.lib.db.model('Employee')(data)

console.log(newEmployee)

newEmployee.save((err, emp) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, emp)

})

} else {

next(this.RESTError('InvalidArgumentError', 'No data received'))

}

update(req, res, next) {

let data = req.body

let id = req.params.id

if(id) {

this.lib.db.model("Employee").findOne({_id: id}).exec((err, emp) => {

if(err) return next(this.RESTError('InternalServerError', err))

emp = Object.assign(emp, data)

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emp.save((err, employee) => {

if(err) return next(this.RESTError('InternalServerError', err))

this.writeHAL(res, employee)

})

} else {

next(this.RESTError('InvalidArgumentError','Invalid id received'))

}

module.exports = function(lib) {

let controller = new Employees(lib);

controller.addAction({

'path': '/employees',

'method': 'GET',

'summary': 'Returns the list of employees across all stores',

'responseClass': 'Employee',

'nickname': 'getEmployees'

}, controller.list)

controller.addAction({

'path': '/employees/{id}',

'method': 'GET',

'params': [swagger.pathParam('id','The id of the

employee','string')],

'summary': 'Returns the data of an employee',

'responseClass': 'Employee',

'nickname': 'getEmployee'

}, controller.details)

controller.addAction({

'path': '/employees',

'method': 'POST',

'params': [swagger.bodyParam('employee', 'The JSON data of the

employee', 'string')],

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228

'summary': 'Adds a new employee to the list',

'responseClass': 'Employee',

'nickname': 'newEmployee'

}, controller.create)

controller.addAction({

'path': '/employees/{id}',

'method': 'PUT',

'summary': "UPDATES an employee's information",

'params': [swagger.pathParam('id','The id of the

employee','string'), swagger.bodyParam('employee',

'The new information to update', 'string')],

'responseClass': 'Employee',

'nickname': 'updateEmployee'

}, controller.update)

return controller

}

lib

As mentioned, the lib folder contains all sorts of helper functions and utilities that were

just too small to be put into a separate folder, but important and generic enough to be

used in several places of the code.

/lib/index.js

Listing 7-11. Code for the Main lib File, which Provides Access to the Exported

Modules

const mongoose = require("mongoose");

module.exports = {

helpers: require("./helpers"),

logger: require("./logger"),

controllers: require("../controllers"),

schemas: require("../schemas"),

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229

schemaValidator: require("./schemaValidator"),

db: require("./db")(mongoose)

}

This file is meant to act as the single point of contact between the outside world

(the rest of the project) and the inside world (all of the mini-modules grouped within

this folder). There is nothing special about it. This file is simply used as a centralizer for

all the require statements you’d use throughout your code if you were to individually

require the specific files. In other words, it just does a require for everything and exports

the returned code using predefined keys.

Listing 7-12. /lib/helpers.js

const halson = require("halson"),

config = require("config");

module.exports = {

makeHAL: makeHAL,

setupRoutes: setupRoutes,

validateKey: validateKey

}

function setupRoutes(server, swagger, lib) {

for(controller in lib.controllers) {

cont = lib.controllers[controller](lib)

cont.setUpActions(server, swagger)

}

/**

Makes sure to sign every request and compare it

against the key sent by the client, this way

we make sure it's authentic

*/

function validateKey(hmacdata, key, lib) {

//This is for testing the swagger-ui, should be removed after

development to avoid possible security problem :)

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230

if(+key == 777) return true

let hmac = require("crypto").createHmac("md5", config.

get('secretKey'))

.update(hmacdata)

.digest("hex");

return hmac == key

}

function makeHAL(data, links, embed) {

let obj = halson(data)

if(links && links.length > 0) {

links.forEach( lnk => {

obj.addLink(lnk.name, {

href: lnk.href,

title: lnk.title || ''

})

}

if(embed && embed.length > 0) {

embed.forEach( item => {

obj.addEmbed(item.name, item.data)

})

}

return obj

}

Just as the modules exported by the index.js file are too small to merit their own

folder, these functions (Listing 7-12) are too small and particular to merit their own

module, so instead they are grouped here, inside the helpers module. The functions are

meant to be of use (hence, the name “helpers”) throughout the entire project.

Let’s quickly go over each of these names:

setupRoutes: This function is called from within the project’s

main file during boot-up time. It’s meant to initialize all

controllers, which in turn adds the actual route’s code to the HTTP

server.

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validateKey: is function contains the code to validate the

request by recalculating the HMAC key. And as mentioned earlier,

it contains the exception to the rule, allowing any request to

validate if the key sent is 777.

makeHAL: is function turns any type of object into a HAL JSON

object ready to be rendered. is particular function is heavily

used from within the models’ code.

Listing 7-13. /lib/schemaValidator.js

const tv4 = require("tv4"),

formats = require("tv4-formats"),

schemas = require("../request_schemas/")

module.exports = {

validateRequest: validate

}

function validate (req) {

let res = {valid: true}

tv4.addFormat(formats)

let schemaKey = req.route ? req.route.path.toString().

replace("/", "") : ''

let actionKey = req.route.name

let mySchema = null,

myData = null;

if(schemas[schemaKey]){

mySchema = schemas[schemaKey][actionKey]

data = null

if(mySchema) {

switch(mySchema.validate) {

case 'params':

data = req.params

break

}

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res = tv4.validateMultiple(data, mySchema.schema)

}

return res

}

This file (Listing 7-13) has the code that validates any request against a JSON Schema

that we define. The only function of interest is the validate function, which validates

the request object. It also counts on a predefined structure inside the request, which is

added by Swagger (the route attribute).

As you might’ve guessed from Listing 7-13 code, the validation of a request is

optional; not every request is being validated. And right now, only query parameters are

validated, but this can be extended by simply adding a new case to the switch statement.

This function works with the premise of “convention over configuration,” which

means that if you set up everything “right,” then you don’t have to do much. In our

particular case, we’re looking inside the request_schemas folder to load a set of

predefined schemas, which have a very specific format. In that format we find the name

of the action (the nickname that we set up) to validate and the portion of the request we

want to validate. In our particular function, we’re only validating query parameters for

things such as invalid formats and so forth. The only request we have set up to validate

right now is the BookSales listing action; but if we wanted to add a new validation, it

would just be a matter of adding a new schema—no programming required.

Listing 7-14. /lib/db.js

const config = require("config"),

_ = require("underscore"),

mongoose = require("mongoose"),

Schema = mongoose.Schema

let obj = {

cachedModels: {},

getModelFromSchema: getModelFromSchema,

model: function(mname) {

return this.models[mname]

},

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connect: function(cb) {

mongoose.connect(config.database.host + "/" + config.

database.dbname)

this.connection = mongoose.connection

this.connection.on('error', cb)

this.connection.on('open', cb)

}

obj.models = require("../models/")(obj)

module.exports = obj

function translateComplexType(v, strType) {

let tmp = null

let type = strType || v['type']

switch(type) {

case 'array':

tmp = []

if(v['items']['$ref'] != null) {

tmp.push({

type: Schema.ObjectId,

ref: v['items']['$ref']

})

} else {

let originalType = v['items']['type']

v['items']['type'] =

translateTypeToJs(v['items']['type'])

tmp.push(translateComplexType(v['items'],

originalType))

}

break;

case 'object':

tmp = {}

let props = v['properties']

_.each(props, (data, k) => {

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234

if(data['$ref'] != null) {

tmp[k] = {

type: Schema.ObjectId,

ref: data['$ref']

}

} else {

tmp[k] = translateTypeToJs

(data['type'])

}

})

break;

default:

tmp = v

tmp['type'] = translateTypeToJs(type)

break;

}

return tmp

}

/**

Turns the JSON Schema into a Mongoose schema

*/

function getModelFromSchema(schema) {

let data = {

schema: {}

}

let newSchema = {}

let tmp = null

_.each(schema.properties, (v, propName) => {

if(v['$ref'] != null) {

tmp = {

type: Schema.Types.ObjectId,

ref: v['$ref']

}

} else {

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235

tmp = translateComplexType(v) //{}

}

newSchema[propName] = tmp

})

data.schema = new Schema(newSchema)

return data

}

function translateTypeToJs(t) {

if(t.indexOf('int') === 0) {

t = "number"

}

return eval(t.charAt(0).toUpperCase() + t.substr(1))

}

Listing 7-14 contains some interesting functions that are used a lot from the models’

code. In Chapter 5 I mentioned that the schemas used with Swagger could potentially

be reused to do other things, such as defining the models’ schemas. But to do this, we

need a function to translate the standard JSON Schema into the nonstandard JSON

format required by Mongoose to define a model. This is where the getModelFromSchema

function comes into play; its code is meant to go over the structure of the JSON Schema

and create a new, simpler JSON structure to be used as a Mongoose Schema.

The other functions are more straightforward:

• connect: Connects to the database server and sets up the callbacks for

both error and success cases

• model: Accesses the model from outside. We could just directly

access the models using the object models, but it’s always a good idea

to provide a wrapper in case you ever need to add extra behaviors

(such as checking for errors).

Finally, as seen in Listing 7-15, the main logging function is defined in this file.

Thanks to the module Winston

3

(which you can add by doing npm install winston

--save) we’re able to define a generic and powerful logger, with a standard output

format for all messages and the possibility of adding the “transports” if needed.

3

See https://www.npmjs.com/package/winston

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236

Listing 7-15. /lib/logger.js

const config = require("config");

let _ENV = process.env.NODE_ENV || config.get('env');

const { createLogger, format, addColors, transports } = require('winston');

const { combine, timestamp, label, printf, colorize } = format;

const myFormat = printf(info => {

return `${info.timestamp} [${info.label}] ${info.level}: ${info.message}`;

});

const myCustomLevels = {

levels: {

error: 0,

warn: 1,

info: 2,

debug: 3,

},

colors: {

error: 'red',

warn: 'yellow',

info: 'blue',

debug: 'violet'

}

};

const logger = createLogger({

format: combine(

colorize(),

label({ label: _ENV }),

timestamp(),

myFormat

),

levels: myCustomLevels.levels,

transports: [new transports.Console()]

});

CHAPTER 7 DEVELOPING YOUR REST API

237

addColors(myCustomLevels)

module.exports = logger;

By default, the code assumes the environment set on the default configuration file.

This value can be overridden by setting a value for the environment variable NODE_ENV.

Models

This folder contains the actual code of each model. The definition of these resources

won’t be found in these files because they’re only meant to define behavior. The actual

properties are defined in the schemas folder (which, again, is being used both by the

models and Swagger).

Listing 7-16. /models/index.js

module.exports = function(db) {

return {

"Book": require("./book")(db),

"Booksale": require("./booksale")(db),

"ClientReview": require("./clientreview")(db),

"Client": require("./client")(db),

"Employee": require("./employee")(db),

"Store": require("./store")(db),

"Author": require("./author")(db)

}

Again, as in the other folders, the index.js file (seen in Listing 7-16) allows us to

require every model at once and treat this folder like a module itself. The other thing

of note here is the passing of the db object to every model, so that they can access the

getModelFromSchema function.

Listing 7-17. /models/author.js

const mongoose = require("mongoose")

jsonSelect = require('mongoose-json-select'),

helpers = require("../lib/helpers");

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238

module.exports = function(db) {

let schema = require("../schemas/author.js")

let modelDef = db.getModelFromSchema(schema)

modelDef.schema.plugin(jsonSelect, '-books')

modelDef.schema.methods.toHAL = function() {

let halObj = helpers.makeHAL(this.toJSON(),

[{name: 'books',

'href': '/authors/' + this.id + '/books', 'title': 'Books'}])

if(this.books.length > 0) {

if(this.books[0].toString().length != 24) {

halObj.addEmbed('books', this.books.map

(e => { return e.toHAL() }))

}

return halObj

}

return mongoose.model(modelDef.name, modelDef.schema)

}

Listing 7-17 shows the basic mechanics of loading the JSON Schema, transforming

it into a Mongoose Schema, defining the custom behavior, and finally returning a new

model.

The following defines the main custom behaviors:

• The jsonSelect model allows us to define the attributes to add to

or remove from the object when turning it into a JSON.We want

to remove the embedded objects from the JSON representation,

because they will be added to the HAL JSON representation as

embedded objects, rather than being part of the main object.

• e toHAL method takes care of returning the representation of the

resource in HAL JSON format.

• e links associated to the main object are dened manually. We

could improve this by further customizing the code for the loading

and transformation of the JSON Schemas of the models.

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239

Note Checks like the following (inside the toHAL method) are meant to

determine if the model has populated a reference, or if it is simply the id of the

referenced object:

if(this.books[0].toString().length != 24) {

//...

}

The following is the rest of the code inside the models folder; as you can appreciate,

the same mechanics are duplicated on every case.

Listing 7-18. /models/book.js

const mongoose = require("mongoose"),

jsonSelect = require('mongoose-json-select'),

helpers = require("../lib/helpers")

module.exports = function(db) {

let schema = require("../schemas/book.js")

let modelDef = db.getModelFromSchema(schema)

modelDef.schema.plugin(jsonSelect, '-stores -authors')

modelDef.schema.methods.toHAL = function() {

let halObj = helpers.makeHAL(this.toJSON(),

[{name: 'reviews',

href: '/books/' + this.

id + '/reviews', title:

'Reviews'}])

if(this.stores.length > 0) {

if(this.stores[0].store.toString().length != 24) {

halObj.addEmbed('stores', this.stores.

map(s => { return { store: s.store.toHAL(),

copies: s.copies } } ))

}

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240

if(this.authors.length > 0) {

if(this.authors[0].toString().length != 24) {

halObj.addEmbed('authors', this.authors)

}

return halObj

}

return mongoose.model(modelDef.name, modelDef.schema)

}

Listing 7-19. /models/booksale.js

const mongoose = require("mongoose"),

jsonSelect = require('mongoose-json-select'),

helpers = require("../lib/helpers");

module.exports = db => {

let schema = require("../schemas/booksale.js")

let modelDef = db.getModelFromSchema(schema)

modelDef.schema.plugin(jsonSelect, '-store -employee -client

-books')

modelDef.schema.methods.toHAL = function() {

let halObj = helpers.makeHAL(this.toJSON());

['books', 'store', 'employee', 'client']

.filter( prop => {

if(Array.isArray(this[prop])) return

this[prop][0].toString().length != 24;

return this[prop].toString().length != 24

})

.map( prop => {

if(Array.isArray(this[prop])) halObj.

addEmbed(prop, this[prop].map(p => { return

p.toHAL()}))

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241

else halObj.addEmbed(prop, this[prop].

toHAL())

})

return halObj

}

return mongoose.model(modelDef.name, modelDef.schema)

}

Listing 7-20. /models/client.js

const mongoose = require("mongoose"),

jsonSelect = require('mongoose-json-select'),

helpers = require("../lib/helpers");

module.exports = db => {

let schema = require("../schemas/client.js")

let modelDef = db.getModelFromSchema(schema)

modelDef.schema.methods.toHAL = function() {

return helpers.makeHAL(this.toJSON())

}

return mongoose.model(modelDef.name, modelDef.schema)

}

Listing 7-21. /models/clientreview.js

const mongoose = require("mongoose"),

jsonSelect = require('mongoose-json-select'),

helpers = require("../lib/helpers");

module.exports = db => {

let schema = require("../schemas/clientreview.js")

let modelDef = db.getModelFromSchema(schema)

modelDef.schema.methods.toHAL = function() {

return helpers.makeHAL(this.toJSON())

}

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242

modelDef.schema.post('save', function(doc, next) {

db.model('Book').update({_id: doc.book}, {$addToSet:

{reviews: this.id}}, next)

})

return mongoose.model(modelDef.name, modelDef.schema)

}

Listing 7-22. /models/employee.js

const mongoose = require("mongoose"),

jsonSelect = require('mongoose-json-select'),

helpers = require("../lib/helpers");

module.exports = db => {

let schema = require("../schemas/employee.js")

let modelDef = db.getModelFromSchema(schema)

modelDef.schema.methods.toHAL = function() {

let json = JSON.stringify(this) //toJSON()

return helpers.makeHAL(json);

}

return mongoose.model(modelDef.name, modelDef.schema)

}

Listing 7-23. /models/store.js

const mongoose = require("mongoose"),

jsonSelect = require("mongoose-json-select"),

helpers = require("../lib/helpers")

module.exports = db => {

let schema = require("../schemas/store.js")

let modelDef = db.getModelFromSchema(schema)

modelDef.schema.plugin(jsonSelect, '-employees')

modelDef.schema.methods.toHAL = function() {

let halObj = helpers.makeHAL(this.toJSON(),

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243

[{name: 'books', href: '/

stores/' + this.id + '/

books', title: 'Books'},

{name: 'employees',

href: '/stores/' + this.

id + '/employees', title:

'Employees'},

{name: 'booksales', href: '/

stores/' + this.id + '/booksales',

title: 'Book Sales'}])

if(this.employees.length > 0) {

if(this.employees[0].toString().length != 24) {

halObj.addEmbed('employees', this.

employees.map(e => { return e.toHAL() }))

}

return halObj

}

return mongoose.model(modelDef.name, modelDef.schema);

}

request_schemas

This folder contains the JSON Schemas that will be used to validate the requests. They

need to describe an object and its properties. We should be able to validate against the

request object attribute that contains the parameters (normally request.params, but

potentially something else, such as request.body).

Due to the type of attributes we defined for our endpoints, there is really only one

endpoint that we would want to validate: the getBookSales (GET /booksales) endpoint.

It receives two date parameters, and we probably want to validate their format to be

100% certain that the dates are valid.

Again, to provide the simplicity of usage that “convention over configuration”

provides, our schema files must follow a very specific format, which is then used by the

validator that we saw earlier (see Listing 7-13).

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244

Listing 7-24. Template Code for a Validator

/request_schemas/[CONTROLLER NAME].js

module.exports = {

[ENDPOINT NICKNAME]: {

validate: [TYPE],

schema: [JSON SCHEMA]

}

There are several pieces that need to be explained in the preceding code:

• CONTROLLER NAME: This means that the file for the schema needs

to have the same name as the controller, all lowercase. And since we

already did that for our controllers’ files, this means the schemas for

each controller will have to have the same name as each controller’s

file.

• ENDPOINT NICKNAME: is should be the nickname given to

the action when adding it to the controller (using the addAction

method).

• TYPE: e type of object to validate. e only value supported right

now is params, which references the query and path parameters

received. is could be extended to support other objects.

• JSON SCHEMA: This is where we add the actual JSON Schema

defining the request parameters.

Listing 7-25 shows the actual code defining the validation for the getBookSales

action.

Listing 7-25. /request_schemas/booksales.js

module.exports = {

getbooksales: {

validate: 'params',

schema: {

CHAPTER 7 DEVELOPING YOUR REST API

245

type: "object",

properties: {

start_date: {

type: 'string',

format:'date'

},

end_date: {

type: 'string',

format:'date'

},

store_id: {

type: 'string'

}

schemas

This folder contains the JSON Schema definitions of our resources, which also translate

into the Mongoose Schemas when initializing our models.

The level of detail provided in these files is very important, because it also translates

into the actual Mongoose model. This means that we could define things such as ranges

of values and format patterns, which would be validated by Mongoose when creating the

new resources.

For instance, let’s take a look at ClientReview, a schema that makes use of such

capability.

Listing 7-26. /schemas/clientreview.js

module.exports = {

"id": "ClientReview",

"properties": {

"client": {

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246

"$ref": "Client",

"description": "The client who submits the review"

},

"book": {

"$ref": "Book",

"description": "The book being reviewed"

},

"review_text": {

"type": "string",

"description": "The actual review text"

},

"stars": {

"type": "integer",

"description": "The number of stars, from 0 to 5",

"min": 0,

"max": 5

}

The stars attribute is clearly setting the maximum and minimum values that we can

send when saving a new review. If we tried to send an invalid number, then we would get

an error like the one shown in Figure7-2.

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247

When defining schemas that reference others, remember to correctly name the

reference (the name of each schema is given by the id property). So if you correctly set up

the reference, the getModelFromSchema method of the db module will also properly set up

the reference in Mongoose (this works both for direct reference and for collections).

Listing 7-27 shows the main file for this folder; the index.js works like the index files

in the other folders.

Listing 7-27. schemas/index.js

module.exports = {

models: {

BookSale: require("./booksale"),

Book: require("./book"),

Author: require("./author"),

Store: require("./store"),

Employee: require("./employee"),

Client: require("./client"),

ClientReview: require("./clientreview")

}

Figure 7-2. An error when trying to save an invalid value in a validated model

CHAPTER 7 DEVELOPING YOUR REST API

248

Finally, Listings 7-28 to 7-34 show the rest of the schemas defined for the project.

Listing 7-28. /schemas/author.js

module.exports = {

"id": "Author",

"properties": {

"name": {

"type": "string",

"description": "The full name of the author"

},

"description": {

"type": "string",

"description": "A small bio of the author"

},

"books": {

"type": "array",

"description": "The list of books published on at

least one of the stores by this author",

"items": {

"$ref": "Book"

}

},

"website": {

"type": "string",

"description": "The Website url of the author"

},

"avatar": {

"type": "string",

"description": "The url for the avatar of this

author"

}

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249

Listing 7-29. /schemas/book.js

module.exports = {

"id": "Book",

"properties": {

"title": {

"type": "string",

"description": "The title of the book"

},

"authors": {

"type":"array",

"description":"List of authors of the book",

"items": {

"$ref": "Author"

}

},

"isbn_code": {

"description": "Unique identifier code of the

book",

"type":"string"

},

"stores": {

"type": "array",

"description": "The stores where clients can buy

this book",

"items": {

"type": "object",

"properties": {

"store": {

"$ref": "Store",

},

"copies": {

"type": "integer"

}

CHAPTER 7 DEVELOPING YOUR REST API

250

}

},

"genre": {

"type": "string",

"description": "Genre of the book"

},

"description": {

"type": "string",

"description": "Description of the book"

},

"reviews": {

"type": "array",

"items": {

"$ref": "ClientReview"

}

},

"price": {

"type": "number",

"minimun": 0,

"description": "The price of this book"

}

Listing 7-30. /schemas/booksale.js

module.exports = {

"id": "BookSale",

"properties": {

"date": {

"type":"date",

"description": "Date of the transaction"

},

"books": {

"type": "array",

"description": "Books sold",

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251

"items": {

"$ref": "Book"

}

},

"store": {

"type": "object",

"description": "The store where this sale took

place",

"type": "object",

"$ref": "Store"

},

"employee": {

"type": "object",

"description": "The employee who makes the sale",

"$ref": "Employee"

},

"client": {

"type": "object",

"description": "The person who gets the books",

"$ref": "Client",

},

"totalAmount": {

"type": "integer"

}

Listing 7-31. /schemas/client.js

module.exports = {

"id": "Client",

"properties": {

"name": {

"type": "string",

"description": "Full name of the client"

},

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"address": {

"type": "string",

"description": "Address of residence of this

client"

},

"phone_number": {

"type": "string",

"description": "Contact phone number for the

client"

},

"email": {

"type": "string",

"description": "Email of the client"

}

Listing 7-32. /schemas/employee.js

module.exports = {

"id": "Employee",

"properties": {

"first_name": {

"type": "string",

"description": "First name of the employee"

},

"last_name": {

"type": "string",

"description": "Last name of the employee"

},

"birthdate": {

"type": "string",

"description": "Date of birth of this employee"

},

"address": {

"type": "string",

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"description": "Address for the employee"

},

"phone_numbers": {

"type": "array",

"description": "List of phone numbers of this

employee",

"items": {

"type": "string"

}

},

"email": {

"type": "string",

"description": "Employee's email"

},

"hire_date": {

"type": "string",

"description": "Date when this employee was hired"

},

"employee_number": {

"type": "number",

"description": "Unique identifier of the employee"

}

Listing 7-33. /schemas/store.js

module.exports = {

"id": "Store",

"properties": {

"name": {

"type": "string",

"description": "The actual name of the store"

},

"address": {

"type": "string",

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254

"description": "The address of the store"

},

"state": {

"type": "string",

"description": "The state where the store resides"

},

"phone_numbers": {

"type": "array",

"description": "List of phone numbers for the

store",

"items": {

"type": "string"

}

},

"employees": {

"type": "array",

"description": "List of employees of the store",

"items": {

"$ref": "Employee"

}

swagger-ui

This folder contains the downloaded Swagger UI project, so we will not go over this

particular code; however, I will mention the minor modifications we’ll need to do to the

index.html file (located at the root of the swagger-ui folder) to get the UI to properly load.

The changes needed are three very simple ones:

1. Edit the routes for all the resources loaded (CSS and JS files) to

start with /swagger- ui/. In other words, all loaded resources

should look like the following:

rel='stylesheet' type='text/css'/>

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2. Change the URL for the documentation server to http://

localhost:9000/api-docs (around line 31).

3. Uncomment the block of code in line 73. Set the right value to the

apiKey variable (set it to 777).

With those changes, the UI should be able to load correctly and allow you to start

testing your API.

Root Folder

This is the root of the project. There are only two files here: the main index.js and the

package.json file that contains the dependencies and other project attributes.

Listing 7-34. /package.json

{

"name": "come_n_read",

"version": "1.0.0",

"description": "",

"main": "index.js",

"scripts": {

"test": "echo \"Error: no test specified\" && exit 1"

},

"author": "",

"license": "ISC",

"dependencies": {

"colors": "^1.0.3",

"config": "^1.30.0",

"halson": "^2.3.1",

"mongoose": "^5.0.0",

"mongoose-json-select": "^0.2.1",

"mongoose-mock": "^0.4.0",

"proxyquire": "^2.0.1",

"restify": "^6.0.0",

"restify-errors": "^6.0.0",

"restify-plugins": "^1.6.0",

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256

"sinon": "^4.5.0",

"swagger-node-restify": "^0.1.2",

"tv4": "^1.1.9",

"tv4-formats": "^1.0.0",

"underscore": "^1.7.0",

"winston": "^3.0.0-rc2"

}

The most interesting part of this file is the list of dependencies. The rest was

autogenerated using the init option of the npm command-line tool.

Tip If you’re testing out the code for this chapter, make sure you install all

dependencies listed in this file by running npm install from the root of the

project’s folder.

Listing 7-35. /index.js

const restify = require("restify"),

restifyPlugins = restify.plugins,

colors = require("colors"),

lib = require("./lib"),

swagger = require("swagger-node-restify"),

config = require("config");

const server = restify.createServer(config.get('server'))

server.use(restifyPlugins.queryParser({

mapParams: true

}))

server.use(restifyPlugins.bodyParser())

restify.defaultResponseHeaders = data => {

this.header('Access-Control-Allow-Origin', '*')

}

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257

///Middleware to check for valid api key sent

server.use((req, res, next) => {

//We move forward if we're dealing with the swagger-ui

or a valid key

if(req.url.indexOf("swagger-ui") != -1 || lib.helpers.

validateKey(req.headers.hmacdata || '', req.params.api_key, lib)) {

next()

} else {

res.send(401, { error: true, msg: 'Invalid api key sent'})

}

})

/**

Validate each request, as long as there is a schema for it

*/

server.use((req, res, next) => {

let results = lib.schemaValidator.validateRequest(req)

if(results.valid) {

return next()

}

res.send(400, results)

})

//the swagger-ui is inside the "swagger-ui" folder

server.get(/^\/swagger-ui(\/.*)?/, restifyPlugins.serveStatic({

directory: __dirname + '/',

default: 'index.html'

}))

swagger.addModels(lib.schemas)

swagger.setAppHandler(server)

lib.helpers.setupRoutes(server, swagger, lib)

swagger.configureSwaggerPaths("", "/api-docs", "") //we remove the {format}

part of the paths, to

swagger.configure('http://localhost:9000', '0.1')

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258

server.listen(config.get('server.port'), () => {

lib.logger.info("Server started succesfully...")

lib.db.connect( err => {

if(err) lib.logger.error("Error trying to connect to

database: ", err)

else lib.logger.info("Database service successfully started")

})

And finally, the main file, the one that starts it all up is the index.js. There are four

distinct sections to this file:

1. e initial section, which requires all needed modules and

instantiates the server.

2. e middleware setup section, which handles setting up all pieces

of middleware (we’ll go over this in a bit).

3. e setup section, which handles loading models, controllers,

setting up routes, and whatnot.

4. e server start section, which starts the web server and the

database client.

The initial and final sections of the file don’t really require much explanation since

they’re pretty self-explanatory, so let’s go over the other two.

Middleware Setup

The middleware setup is potentially the most important part of the file and of the

bootstrap process required for the API to start up and function properly. But thanks to

the ease of use and simplicity that the middleware mechanics bring to the table, it’s very

easy to write and understand.

We’re setting up five different middleware here:

1. e query parser to turn the query parameters into an object so

that we can access them easily

2. e body parser so that we can access the content of the POST and

PUT requests as an object, with the added bonus of autoparsing

JSON strings

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3. e security check, which takes care of rehashing the request every

time to make sure that we’re dealing with an authenticated client

4. e validate check, which validates the request against any

existing JSON Schema

5. e static content folder, which is not exactly a middleware, but

acts as one for one specic set of routes, allowing Restify to serve

static content

Setup Section

This last section is also very important; those five lines actually handle instantiating all

the models, linking Swagger and the Restify server, setting up all the routes (linking the

code of each action to the corresponding path and method defined in the spec section),

and, finally, setting up the route for the Swagger back-end server.

Summary

Congratulations! You should now have a working version of our API, capable of doing

pretty much everything we set up to do in Chapter 6. You should also have a better

understanding of how these modules work. Ideally, you’ll consider them for your next

project. Of course, there are alternatives like the ones discussed in Chapter 5, so don’t

forget about those either.

In the final chapter of the book, I’ll go over some of the most common issues you

might encounter when dealing with this type of project, and you’ll see how to solve

them.

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F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1_8

CHAPTER 8

Testing your API

It’s time to take a small break from REST and API design to discuss something equally

important for your project: how are you going to test it?

The entire point of this chapter is to give you a little insight into what we normally

mean by “testing” in the context of software development. I’ll cover some basic

principles such as unit testing, mocking, and so forth, and once you’re ready, we’ll go

over some examples of how to implement those concepts in your Node.js project.

So let’s get started.

Testing 101

First things first: I’m going to be covering unit testing in this chapter, but if by the end of

it you want to know more, please feel free to go online and keep reading. Honestly, there

is more than enough material about this subject to fill several books. This chapter’s only

aim is to act as an entry way into this world.

The Definition

Let’s start with the basics: at its core, testing in the context of software development is

basically the act of formulating a statement (that should be true) about a piece of code

and adding the required set of assertions to make sure we can prove that said statement

is actually true. So a test can be something like Listing 8-1.

Listing 8-1. Pseudo-Code for a Theoretical Test Case

Statement: "myFunction" is capable of adding up two natural numbers

Assertions:

var a = 10;

var b = 2;

assertion(myFunction(a, b), "is equal to", a + b)

262

We’re not focusing on a specific language right now, so Listing 8-1 is only showing

a pseudo-code attempt at what a test would look like. From that example, I should also

note how I’m testing the function directly; it is a simple example and there is not a lot

of context, but the point here is that your tests shuld focus on the smallest bit of code

that makes sense, instead of testing several things at the same time. Let me explain with

another example in Listing 8-2.

Listing 8-2. Several Different Assertions Inside the Same Test

Statement: "myFunction" can add, multiply and substract two natural numbers

Assertions:

var a = 10

var b = 10

assertion(myFunction("add", a, b), "is equal to", a + b)

assertion(myFunction("multiply", a, b), "is equal to", a * b)

assertion(myFunction("substract", a, b), "is equal to", a – b)

The example is still quite simple, but I’ve added a bit of a more complex internal

logic to the function called myFunction by adding the ability to pass in the mathematical

function to apply as the first parameter. With this new logic, the function we’re testing is

bigger, and it does do different things, so if we design our tests like in Listing 8-2, we can

run into a problem: what happens if our test fails?

I haven’t really covered what it means to “run” our tests, but it should be pretty

obvious by now: your code gets executed and the assertions are verified, if they are true,

then your test will succeed, but if they fail (i.e., your assertion stated two values were to

be equal and, in practice, they aren’t) then your entire test fails. You can see how that can

be a problem if you’re actually testing several things inside the same test. Once you get

the results back from the execution, you’ll have to dig deeper into the execution logs

(if there are any) to actually understand where your problem lies.

To properly test a function like the new myFunction, you’d be better off by splitting

your test case (which is how you call a single test) into three different ones, as seen in

Listing 8-3:

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Listing 8-3. Correct Way to Structure Test Cases When the Function Tested is

Too Complex

Statement: "myFunction" can add two natural numbers

var a = 10

var b = 10

assertion(myFunction("add", a, b), "is equal to", a+b)

Statement: "myFunction" can multiply two natural numbers

var a = 10

var b = 10

assertion(myFunction("multiply", a, b), "is equal to", a*b)

Statement: "myFunction" can substract two natural numbers

var a = 10

var b = 10

assertion(myFunction("substract", a, b), "is equal to", a-b)

Now whenever your tests fails, you’ll get better details from your test runner, because

you’ll know exactly which test failed, and thus, you’ll be able to immediatly determine

which block of code inside your complex function failed.

So to recap and to give you more of a technical definition of what unit testing is, from

everything I’ve shown you so far, you could probably say that:

A unit test is a statement about a unit of code that needs to be proven true

in order to pass.

And the word unit is probably the most important one, because if you go online,

you’ll probably find a lot of people defining it (in this context of course) as your functions

(provided you’re using a procedural programming language) or your methods (if you’re

on an OOP language). But as you can see from a simple generic and pseudo-code-

based example, a unit of code can actually be smaller than that. It’s true that in all these

examples I didn’t really show the actual code of the function, and you could argue that

for each test case of Listing 8-3, our function is actually calling other, smaller functions,

and that is a very good point!

But, there is also probably code tying all those calls together (some kind of logic

based on the value of your first parameter), so if you were to individually test those

smaller functions instead, you’d be missing possible bugs. So if we go back to our

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definition of unit, you’d probably want something like the following (in the context of

software testing ofcourse):

A unit of code is the smallest block of code that makes sense to test and

would allow you to cover a whole logical path.

So putting both definitions together, you get a pretty acurate idea of what testing your

code means and a good basis for the rest of this chapter.

The Tools

Now that we’ve covered what it is, let’s review the tools provided by this methodology

that will allow you to test your code.

These are not software tools, these aren’t libraries or frameworks you can use, we’re

not there yet. What I’m trying to give you here are the wheels you’ll use to build your car

down the road.

Test Cases & Test Suites

Test cases have already been covered, but to reiterate, it is how you call the actual test.

You normally structure them to test a very specific scenario, which is why normally you’d

need several cases before being sure you’ve properly covered every logical path inside

your code.

Test suites are, as their name implies, groups of test cases. Depending on your system

and your methodology, you might want to have a single test suite for all your tests or a

set of suites, acting as logical groups for your unit tests. The criteria used for the suites is

all up to you and your team, so feel free to use this tool to organize your code as much as

you can.

Assertions

I’ve already used this concept in the previous section without formally defining because

it’s one of those things you don’t really need to define before people can understand it.

That being said, there are still some details I left out, so let me cover them here.

Assertions bring meaning to your test cases, everything else inside your test is just

preparation for this line(s) of code. In other words, you first set everything up (function

imports, variables, correct values, etc), and then state your assumptions about the

outcome of the tested code, and that is your assertion.

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If you want to get a bit more technical, an assertion is (usually) a function or method

that executes your target code with the right parameters and checks its output against

your expectations. If they match, then it makes your test pass; if they don’t, then it spits

out an error using the information it knows about your test (description, function called,

expected value, and actual value are some of the most common ones).

You don’t usually need to worry about creating assertions. They are part of every

testing framework and library out there, all you need to know is how to use them, and

that will depend on each implementation. Usually testing frameworks provide several

flavors of assertions to help make the test cases’ code more readable. So you might find

yourself using assertions called isTrue, isEqual, notEqual, throwsException and

other similar names, instead of using just one like in my previous examples. They are of

course syntactic sugar, but when it comes to test development, making them readable

and easy to understand is considered a very good practice.

And since we’re in the topic of good practice for assertions, it is also considered a

very good one to structure your test cases in a way that you only have one assertion per

test. This will help you to:

• Keep your test’s code clean and simple.

• Help the code to be readable.

• Simplify debugging when one of the tests fails, since there is only one

thing that can fail per test.

Stubs, Mocks, Spies, andDummies

These are all similar tools, so I wanted to cover them as part of the same section since

they’re all related in one way or another. It’s important to note that so far the examples

provided in this chapter have been quite simple and naive. Usually production systems

aren’t that straighforward, your methods and functions will normally interact with each

other and other external services (such as APIs, Databases, even the filesystem). This is

why this set of particular tools will help you out in that aspect.

One key mantra that you need to repeat over and over when writing tests is:

I shall not test code that’s already been tested by others

And even though in theory it’s quite obvious (I mean, why would you? Really?), in

practice, the line is sometimes a little blurry. One very common case, especially when

writing public APIs, is to use databases; your CRUD methods, for instance, will most

likely be 80% database interaction, so should you test that code? The answer is “not

entirely.” Let me give you an example with Listing 8-4:

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Listing 8-4. Generic “Save” Function Interacting with Your Database

function savePerson(person) {

if(validationFunction(person)) {

query = createSavePersonQuery(person)

return executeQuery(query)

} else {

return false

}

Listing 8-4 shows a very basic database interaction, you have several functions

there that you probably already tested individually because of their complexity

(validationFunction and createSavePersonQuery) and you also have a function called

executeQuery, which in our case is provided by your database library. You didn’t write

that function, you don’t even have access to its code, so why would you care about

testing it? You can’t really do anything about it if it fails.

More so, why would you even consider depending on your database server being up

and running? Are you going to be using the production database for your tests? What will

you do with the garbage data generated by your tests? What if your database server is up,

but your table is not created? Will the test fail? Should it?

These are all normal questions that arise when starting to write tests and hitting

the brick wall that is reality. If you’re not just starting with tests, but with software

development in general you might think that the right way to go is to have a “test

database,” one you can control and you can do whatever you want with. Heck! I’ve done

it, it’s completely normal, but also wrong.

You see, when you add an external service into your tests, even one you think you

can control such as your own database server, you’re implicitely testing that service and

the connectivity between both systems inside your unit test. You’ve turned a simple

and straightforward test into a very complex one that is not even prepared to handle

everything that could go wrong. What if your network fails? Should this test fail? What

if you forgot to start your db server? Should this test fail too? See where I’m going with

this? And I’m just giving you one simple example, one database. I’m not covering

logging, other APIs, multiple database queries, and so forth. You definitely need to cut

all connections to the outside when unit testing, and that means everything that is not

your target unit of code (or put another way, each test that you write should take care

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267

of only one unit of code and nothing else). Fear not though, because here is where this

particular set of tools comes into play.

Stubs

Let’s say your target unit of code for a particular test depends on another function call,

so whatever that function returns, your code will react accordingly. And you need to

add tests for all the possible reactions, how can you ensure the function you depend on

actually returns what you want?

One possible solution would be to simply use the “right” values, if you already know

how this function behaves, you can do that, but if someone else changes the function in

the future, your tests will fail, because they depend on the actual implementation of an

external function.

Enter stubs, these guys help you deal with external services (or more like external

function calls) by replacing the code that uses them with a simpler version that instead,

returns a known and controlled value. Or, put another way, you can re-write the

functions you depend on to make sure they return the value you expect them to.

You can stub a function or a method in a particular object (as long as the language

lets you), so instead of controlling the database and its content (like in the previous

example), you would overwrite the function that does the actual query with one that

controls the output to whatever you need it to be (as seen in Listing 8-5). This way you

can safely test all possible cases (including those when the network connectivity fails, or

the database is down).

Listing 8-5. Pseudo-Code Examples of How Stubs Help Your Tests

Statement: when the person is saved, the function should return TRUE

Stub: executeQuery(q) { return TRUE } //we assume the query execution went

well

var person = {name: "Fernando Doglio", age: 34}

assertion(savePerson(person), "equals to", TRUE)

Statement: when the person’s data is not valid, the function should return

FALSE

Stub: validationFunction(data) {return FALSE} //we need the validation to

fail in this case

var person = {name: "Fernando Doglio", age: 34}

assertion(savePerson(person), "equals to", FALSE)

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268

Listing 8-5 shows two examples of why stubs are so useful. The first one shows

how you can easily control the outcome of the interaction with an external service;

you don’t need complex logic inside your stubs, the important part on them is their

returned value. The second example is not overwriting an external service, but, rather,

an external function—in fact, one that you probably wrote. And the reason for that

(instead of simply providing an invalid person object as input) is that in the future, your

validation code could change; maybe you added or removed valid parameters from your

person definition, and now your test could fail, not due to the code you’re testing but

to an unwanted side effect. So instead of suffering from that, you simply eliminate the

dependency on that function and make sure that no matter what happens to the internal

logic of validationFunction, you’ll always handle the FALSE output correctly.

In fact, both examples from Listing 8-5 show the two most common uses for stubs:

1. Removing dependency from external service

2. Forcing a logical path inside your target test code

Mocks

Mocks are very similar to stubs, so much so in fact, that many people use both terms to

refer to the same behavior. But that is not correct, even though they’re both conceptually

similar, they are also different.

While stubs allow you to replace or redefine a function or a method (or even an

entire object, why not?), mocks allow you to set expected behaviors on real objects/

functions. So you’re not technically replacing the object or function, you’re just telling

it what to do in some very specific cases. Other than that, the object remains working as

usual.

Let’s look at Listing 8-6 to understand the definition.

Listing 8-6. Example of How a Mock Could Be Used Inside a Test Case

Statement: When replenishing the diapers aisle, the same amount added needs

to be removed from the inventory

Code:

var inventory = Mock(Inventory("diapers"))

//set expectations

inventory

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269

.expect("getItems", 100)

.returns(TRUE)

.expect("removeFromInventory", 100)

.returns(TRUE)

var aisle = Aisle("diapers")

aisle.setRequiredItems(100)

aisle.replenish(inventory) //executes the normal flow

assertion(aisle.isFull(),"equals to", TRUE)

assertion(inventory.verifiedBehavior, "equals to", TRUE)

I know, I know, two assertions inside the same test case. I haven’t even finished the

chapter and I’m already going against my words. Bear with me here, in some cases the

expected behavior for mocks is automatically checked by whatever framework you’re

using, so this example is just to let you know it’s happening. Now get off my back!

Now, back to the example on Listing 8-6, we could’ve definitely done this with

stubs too, but we’re conceptually testing something different. Not just the final state of

the aisle object, but also the way that the aisle object interacts with the inventory,

which is a bit harder to do with stubs. During the first part of the test, where we set the

expectations, we’re basically telling the mocked object, that its getItems method should

be called with a 100 as a parameter and that when it happens, it should return TRUE.

We’re also telling it that its removeFromInventory method should be called with a 100 as

parameter and to return TRUE when this happens. In the end, we’re just checking to see if

that actually happened.

Spies

As cool as this name might sound to you, we’re still dealing with special objects for your

test cases. This particular type of object is an evolution of the stubs. And the reason

why I’m just mentioning it is because spies are the answer to the example on the mock

section.

In other words, spies are stubs that gather execution information, so they can tell

you, at the end, what got called, when, and with which parameters. There is not much

to them, we can look at another example (see Listing 8-7) where you’d need to know

information about the execution of a function in order to show you how you could test it

with spies.

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Listing 8-7. Example of a Spy Being Used to Determine if a Method was Called

Statement: FileReader should close the open file after it’s done.

Code:

var filename = "yourfile.txt"

var myspy = new Spy(IOModule, "openFile") //create a spy for the method

openFile in the module dedicated to I/O

var reader = new FileReader(filename, IOModule)

reader.read()

assertion(myspy.calledWith(filename), "equals to", TRUE)

The example in Listing 8-7 should probably be one of many tests for the FileReader

module, but it exemplifies when a spy can come in handy. In this particular example,

we’re making sure the right method is called to open a file, and that we’re passing it the

right value (the content of the filename variable).

Note The spy, unlike the stub, wraps the target method/function, instead of

replacing it, so the original code of your target will also be executed.

Dummies

Dummies are simply objects that serve no real purpose other than being there when

they’re required. They are never really used, but in some cases, such as strongly typed

languages, you might need to create dummy objects for your method calls to be possible.

If you’re creating a stub of a method that receives three parameters, even though

you’re not thinking about using them, you might need to create dummies so they can be

eventually passed to it. This is a very simple case of test utility object, but it’s a name that

also gets mentioned quite a bit, so I thought I’d cover it.

Fixtures

Test fixtures help provide the initial state of your system before your tests get executed.

They come in handy when your tested code depends on several outside sources of data.

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For instance, think of a configuration checker for your system, you could have

fixtures for different versions of your config files, and load one in each test case,

depending on the type of output you’d want to test.

Fixtures are usually loaded before the tests are run and can be unloaded (or reverted

if necessary) after everything has been tested. Usually test frameworks provide specific

instances on the testing flow for these cases, so you just need to add your fixture-related

code in there.

Best Practices

I’ve already covered some of these partially in the previous section of this chapter, but

it’s probably a good idea to review the full list of recommendations when writing tests.

You have to remember that like anything in software development, it’s never a solo effort,

even if you’re the only one writing code right now, you have to think about the future.

So let’s quickly review and recap.

• Consistent: Your test cases need to be consistent, in the sense that no

matter how many times you run them, they always need to return the

same result if the tested code hasn’t changed.

• Atomic: e end result of your tests need to be either a PASS or a

FAIL message; that’s it, there is no middleground here.

• Single responsibility: is one we already discussed. Your tests

should be taking care of one logical path, just one, that way their

output is easy to understand.

• Useful assertion messages: Testing frameworks usually provide a

way for you to enter descriptions of your test suites and test cases,

that way they can be used when a test fails.

• No conditional logic inside it: Again, I mentioned this one in an

earlier section; you don’t want to add complex logic inside the

test case, it is only meant to initialize and verify end results. If you

see yourself adding this type of code into your test cases, then it’s

probably time to split this one into two (or more) new ones.

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• No exception handling (unless that is what you’re looking for):

is one is related to the previous one; if you’re writing tests, you

shouldn’t really care about any exceptions thrown by our code, there

should already be code in place to catch them. Unless, of course,

you’re actually testing that your code throws a specic exception, in

which case, disregard this one.

Testing withNode.js

Now that you’ve got an idea of what unit testing is and the basic concepts behind this

practice, we can move forward with a specific implementation. You’ll see that testing

your code in Node is not hard at all, even without libraries, since the language already

comes with a built-in assertion module ready to be used.

Testing Without Modules

Let me first talk about this option, it’s probably not the way to go, since the provided

module is pretty basic, but if you’re looking for something that’s quick and dirty, this will

do the job.

One of the major things you’ll notice in this library is that it’s missing the rest of the

framework. By requiring it in your code, you only get the assertion support, the rest of

the helper functions will have to come from you or someplace else. That being said, let’s

look into it anyway.

As I already mentioned, this module does not require any kind of installation steps,

since it’s already provided with Node’s installation, and all you have to do to use it is

to require the module assert. After you do so, you’ll gain access to a set of assertion

methods, which basically help you compare two values (or objects).

I’m going to list some of the most interesting ones. If you want the see the full list,

please go to the official documentation.

1

https://nodejs.org/api/assert.html

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ok(value[, message])

This method evaluates value and if it’s truthy, it’ll pass, otherwise it’ll throw an

AssertionError. The message (if set) is set as the message of the exception. This one

performs a simple equality validation (using ==), so if you need to check strict equality,

then you might want to go with the strictEqual method.

When dealing with truthy values, you have to remember what that means for your

specific language. In the case of JavaScript, this is what you’d get when calling ok:

• ok(1) = TRUE

• ok(0) = FALSE

• ok(“hello world!”) = TRUE

• ok(“”) = FALSE

• ok(undened) = FALSE

• ok(3203) = TRUE

• ok(null) = FALSE

deepStrictEqual(actual, expected[, message])

This one performs a deep comparison between two objects. In case you didn’t know,

that means is Node will recursively compare (using the strictly equal operand) properties

inside the objects, and if that comparison fails it’ll throw an AssertionError.

For instance, something like what’s shown on Listing 8-8 would show an error

message.

Listing 8-8. Simple Example of how deepStrictEqual Works

const assert = require("assert")

try {

assert.deepStrictEqual({a: 1}, {a: '1'})

} catch(e) {

console.log(e)

}

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The previous example shows the details of the thrown exception:

Listing 8-9. AssertionError Exception Thrown from the Code of Listing 8-8

{ AssertionError [ERR_ASSERTION]: { a: 1 } deepStrictEqual { a: '1' }

at repl:1:14

at ContextifyScript.Script.runInThisContext (vm.js:44:33)

at REPLServer.defaultEval (repl.js:239:29)

at bound (domain.js:301:14)

at REPLServer.runBound [as eval] (domain.js:314:12)

at REPLServer.onLine (repl.js:433:10)

at emitOne (events.js:120:20)

at REPLServer.emit (events.js:210:7)

at REPLServer.Interface._onLine (readline.js:278:10)

at REPLServer.Interface._line (readline.js:625:8)

generatedMessage: true,

code: 'ERR_ASSERTION',

actual: { a: 1 },

expected: { a: '1' },

operator: 'deepStrictEqual' }

As expected, because in Javascript the number 1 and the string literal ‘1’ aren’t

strictly the same, the objects compared in Listing 8-8 aren’t equal.

Note If instead you were to use the deepEqual method, the comparison from

Listing 8-8 would pass correctly.

throws(block[, error][, message)

The other method I want to highlight is this one, which will test your block of code for

a thrown exception. The only mandatory parameter here is (like the method signature

indicates) the first one, but you can also add pretty interesting behaviors using the

second one.

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For the error parameter, you can use one of several options, such as a constructor

that simply indicates the type of error expected. You can also use a RegEx to validate the

name of the type or, and this is the most crazy you can get with this method, you can

manually check the results by providing a checking function as the second parameter.

Listing 8-10 shows a small example taken directly from Node’s documentation site,

showing how to use a function to check a couple of details about the error thrown.

Listing 8-10. Code Showing Example Using a Function As a Second Parameter

assert.throws(

() => {

throw new Error('Wrong value');

},

function(err) {

if ((err instanceof Error) && /value/.test(err)) {

return true;

}

},

'unexpected error'

);

There are a lot of other methods to use but they’re just variations on the three we

just covered, so I’ll let you browse the documentation to read the whole list of options.

Let’s now look at what it looks like to add tests in Node using one of the most common

libraries out there: Mocha.

Mocha

When it comes to testing libraries for Node, the list is always growing: you have some that

add assertions, others that are full testing frameworks for TDD, others provide the tools

you need if you’re practicing BDD, and I could keep going. So, let’s just focus on one of

them, the one most people in the community seem to be using these days, and see what

testing with it looks like.

So particularily, Mocha

2

is a testing framework (so it’s not just an assertion library,

it actually provides a full set of tools for us) that allows for both asynchronous and

2

https://mochajs.org/

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276

synchrounous testing; so considering asynchronous functions are quite common in

Node.js, this is a great choice already.

Installing andFirst Steps

To install the latest version of Mocha into your system, you can simply use the command

shown in Listing 8-11:

Listing 8-11. Installing Mocha

$ npm install mocha -g

Listing 8-11 will install version 5.1.0 as of the writing of this chapter. Once this is over,

you can proceed to start writing your test cases. Listing 8-12 shows a quick example of one:

Listing 8-12. Sample Test Case Written Using Mocha

const assert = require('assert');

describe('Array', function() {

describe('#indexOf()', function() {

it('should return -1 when the value is not present', function() {

assert.equal([1,2,3].indexOf(4), -1);

});

There are several things to notice from the example on Listing 8-12:

• We’re not directly calling mocha, or requiring the module at all. This

is not needed, because to execute the test, you’ll be using mocha’s cli

tool, which will take care of that.

• We’re back to using the assert module from Node, which is one of

the features from Mocha: it won’t force an assertion syntax on you,

it’ll let you decide which one to use based on your prefererences.

• e describe function can be nested as many times as you need, it’s

just a gruping mechanism that can help you when reading the code

and when looking at the output from mocha (more on this subject in

a minute).

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• Finally, the it function, on the other hand, contains the actual test

case; inside its callback you define the test’s logic.

To run the test, then you simply execute:

$ mocha

and the output should be something like the one shown in Listing 8-13 (provided you saved

your code in a file called test.js, which is where mocha will look by default for your tests):

Listing 8-13. Output from Running Your Mocha Tests

Array

#indexOf()

✓ should return -1 when the value is not present

1 passing (7ms)

Notice the indentation of the first two lines; that’s related to the use of the describe

function.

Testing Asynchronous Code

Before going into the specifics of how to test our project, I’m going to talk about one

more feature provided by Mocha, since it’ll come in super handy: asynchronous tests.

To test asynchronous functions using Mocha, you simply have to add a parameter to

the callback on the it function. This will tell Mocha that the test is asynchronous, and

it’ll know to wait until that parameter is called upon (it’s going to be a function indicating

the end of the test). It is worth noting that this function can only be called once per test,

so if you try (or do so by accident) to call it more than once, your test will fail.

Listing 8-14 provides an example of how this would look.

Listing 8-14. Example of an Asynchronous Test Case in Mocha

describe('User', function() {

describe('#save()', function() {

it('should save without error', function(done) {

var user = new User('Luna');

user.save(function(err) {

if (err) done(err);

else done();

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});

The attribute for the callback is usually called done, to signify the ending of the

particular test case. Finally, this function follows the normal callback pattern, so it

receives the error attribute as the first parameter, thus the code from Listing 8-15 can be

further simplified as follows:

Listing 8-15. Simplified Example of an Asynchronous Test Case

describe('User', function() {

describe('#save()', function() {

it('should save without error', function(done) {

var user = new User('Luna');

user.save(done);

});

There are a ton of other features for this library that I haven’t covered (and won’t

cover) in this chapter, so please, I urge you to go to its main website

3

and browse through

its documentation. Let’s now look at what it would look like to add some tests to our API

project.

Testing Our API

In this section we’re going to cover how to go about adding all the required code into the

existing API project, so that we can test it’s code.

Because of the nature of the API project, there is a lot of repeted code/logic, such

as the create methods, in each one. The same code an eventually be isolated and

individually tested before it gets out of hand.

For the purpose of this exercise and to show you how you can add tests yourself

(applying the concepts we’ve already covered), I’m going to show you how to create tests

for the create method of the BookSales controller.

3

See https://mochajs.org/#table-of-contents

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279

Let’s look at the code first (in Listing 8-16), and then I’ll do a quick overview of what’s

being presented.

Listing 8-16. Unit Tests for the BookSales Controller’s Create Method

const assert = require("assert");

const restifyErrors = require("restify-errors")

const sinon = require("sinon")

const mongoose = require("mongoose")

const lib = require("../lib");

describe("Controllers", function () {

describe("BookSales", function() {

describe("#create", function() {

let BookSales;

//setup all we need for the tests

beforeEach(function() {

BookSales = require("../controllers/

booksales")(lib);

sinon.spy(BookSales, "writeHAL")

})

//and tear down whatever we changed

afterEach(function(){

BookSales.writeHAL.restore();

})

//tests

it("should return an InvalidArgument exception

if no body is provided in the request", function

(done) {

BookSales.create({}, {}, function(err) {

assert.ok(err instanceof

restifyErrors.InvalidArgumentError)

done();

})

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280

it("should call the save method for the booksale

model", function() {

//we'll spy on this method to understand

when and how we call it

sinon.spy(mongoose.Model.prototype, "save")

BookSales.create({body: {totalAmount: 1}}, {})

assert.ok(mongoose.Model.prototype.save.

calledOnce)

mongoose.Model.prototype.save.restore();

})

it("should call the writeHAL method", function() {

//we stub the method, so it can actually

succeed even without a valid connection

sinon.stub(mongoose.Model.prototype,

"save").callsFake( cb => cb() )

//we create a simple fake "json" property

that will be called by writeHAL

BookSales.create({body: {totalAmount: 1}},

{json: () => {} })

assert.ok(BookSales.writeHAL.calledOnce)

mongoose.Model.prototype.save.restore();

})

So we begin by creating the groups for our tests. As I mentioned before, these groups

can be anything we want. In my case I felt Controllers -> [Controller name] -> [Method

name] would come in handy.

After that, for the specific method we’re testing here, we’ll test the following:

• That it throws the correct type of error message whenever the body

for a new book sale is not present

• at it calls the save method on the model being created

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• Finally, that after a successful data save on the database, the

controller is actually calling the writeHAL method, to create the

correctly formatted response

All three tests have different mechanics. The first shows you how to use the done

callback optionally available within each test. If you’re dealing with an asynchronous

function, that’s how you tell it when to actually stop waiting for a response.

The second is actually creating a spy on a method, so we can tell whether or not it

was called. Note that to create the spy, we’re using yet another module called SinonJS

(which you can install by simply doing npm install sinon). This particular library

works together with Mocha (or any other unit testing framework) and provides the of the

mejor tools we saw earlier in this chapter: Mocks, Spies, and Stubs.

Finally, the third test case is creating a stub, because we need to control exactly how

the insertion into the database works (in this case, ending with a successful returned

value as if the database was actually there). This particular test is also not directly

creating and restoring the spy on the writeHAL method for the controller; instead, that

happens inside the beforeEach and afterEach function callbacks, which are part of the

testing flow executed by Mocha. They’re there to move away from the test case’s code

anything that needs to happen for every single test.

Now that we’ve covered the code, let’s quickly look at its output to understand what

you should be aiming to get on your side. First, you execute it with the following line,

assuming you’ve added the code from Listing 8-16 in a folder called “tests” at the root of

your project.

$mocha tests/

And the output should be something like the following:

Figure 8-1. Output of the execution

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In Figure8-1 you can see the other point of having the groups: the results are

much easier to understand if the tests are properly grouped. Also, notice the error

message; even though the tests are all green, we’re showing an error message, and that’s

completely normal, since the very first test is actually testing for the error type.

Summary

This chapter covered a small glimpse into the unit testing world, showing you the basics

to both understand how they work and how to write them, and how to implement them

in Node.js.

In the next chapter, I’m going to cover the actual deployment of your application and

the type of tools you might want to consider using for that.

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F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1_9

CHAPTER 9

Deploying into Production

As the last step in your normal development cycle, you’d want to deploy your brand new

APIs into a production system. This might sound obvious to you (then again, maybe not),

but just because it works on your computer doesn’t mean it’ll work for your customers,

so when deploying into such a specific environment like Production, there are some key

aspects you’d want to consider, and we’ll review those in this chapter.

Finally and to close this chapter, we’ll go over Shipit and PM2—a very interesting pair

of tools to help you keep track of your production deploys.

Different Environments

When working on seriuos software project, basically anything that is intended to see the

light of the public will normally have different stages. In particular, projects that are web-

related, like, say, an API, will have these stages represented as different environments

where the application is deployed.

In these environments, you’ll have different versions of your code deployed and

working, depending on the intended use of each one. Any standard web-related project

will have at least three or maybe four environments to deploy to at any point into their

development cycle.

The Classical Development Workflow

Based off of the content of Table9-1, the classical development cycle for a web-related

project looks something like Figure9-1.

284

Table 9-1. List of Standard Environments for Web-Based Software Projects

Environment Description

Development This environment is usually intended for developers only; here is where they

normally integrate their currently in-progress work and see how it behaves with

the rest of their colleagues’ work. If there is only one developer working on the

project, this could very well be his/her computer (provided the project being

worked on is capable of running on a single computer).

QA (or

sometimes, QC)

After the developer’s work is done and they have deemed it ready, the code

needs to be deployed here. In this environment the quality assurance team (or

whoever is in charge of quality on your team) will review the feature from a

functional point of view (or in other words, without looking at the source code).

UAT (sometimes

this one is

missing)

Also known as User Acceptance Tests, this environment is meant to act as

a pre- production stage, where you’ll have the code that is meant to go to

production soon deployed. At this point your client or a subset of nal customers

will be testing this version of the product. The intention is to catch any issues

that might’ve escaped your developers and your QA/QC team because is more

of a business-related problem than a technical one.

Production Last but certainly not least, production is where your ready-to-be-used code will

live. This is the nal stage of your development cycle.

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285

If everything goes well (which usually never happens, let’s be real here), your code

will go from the Development environment all the way to Production, one environment

at the time. But if there are problems with the delivered code, they should be found

either in the QA environment or in the UAT, although the latter is far from desired, since

that potentially means exposing issues to the final client.

As for how similar or different these environments should be from each other, there

is no real standard here, since that will definitely depend on the type of project you’re

working on, the budget you have, where these environments are located, and a big list of

“etc.” after this. I will, however, give you a basic rule of thumb.

Figure 9-1. Diagram describing a typical development cycle

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Generally speaking, your Development and Production environments are

diametrically opposite; they have completely different intended audiences and

availability requirements, so having them be different is not a big deal. In a continuous

deployment scenario, the development environment is the one that gets the most action,

so having it be simpler (from an infrastructure point of view) might help lower the

maintenance costs and the deployment times as well.

As for QA and UAT, they’re in the middle, and depending on your reality, it might

be a good idea to have QA be similar to DEV, since (a) it is going to be the second most

active environment (from a deployment point of view, of course), and (b) it might help

developers debug errors they can’t find in their own environments. On the other hand,

it’s usually a good idea to have UAT be like Production, since any infrastructure-related

bugs should ideally be detected before reaching the final stage.

Again, take this with a grain of salt and adapt it to your reality.

Tips forYour Production Environment

There are certain aspects to consider when defining the architecture of your production

environment, although they might depend on the type of project you’re creating.

High Availability

If you’re going after high availablity, you’re basically asking for your platform/system to

stay functional in the face of disaster or, put simpler, when parts of your modules start

failing due to technical problems.

Don’t get me wrong, this subject alone is quite big and could fill up several chapters; I’m

just doing a very high-level introduction and describing a couple of techniques that might

come in handy when you start thinking about going live, and those are: load- balancing your

web servers and thinking about zone availability. Let me go into a bit more details on them.

Load Balancers

On any normal and successful application that starts being massively used, your

incoming traffic will become a problem if you’re not prepared for it.

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This traffic will start overloading your servers first, and when this happens, you’ll

either have to scale up vertically or horizontally. Vertical scale implies adding more

resources to your servers (memory or disc, for instance) but that (obviously) has its

limits. Eventually this strategy will not be enough.

Horizontal scaling, however, implies adding more computing power by adding more

computers (or, in this case, servers). This is the better option if you know your traffic can

keep growing to exceed the capacity of just one server, but is also adds extra problems.

When you have several web servers for your client-facing application, how do you

distribute the load among them? This is where load balancer comes in.

Load balancers are software products you can install on your server, and they will

(if properly configured) distribute incoming traffic into your array of servers. Some

common load balancers are ELB from Amazon, F5 Networks, and Nginx (yes, the

web server can also be configured as a load balancer). These load balancers work by

distributing incoming traffic based on a pre-defined set of rules, such as:

• Round robin: With every new request the balancer would hit a new

server, and it’ll keep going by cycling to the first one.

• Least connected: Next incoming request will go to the server with the

least number of active connections

• IP hash function: Hashing function of the client’s IP address,

assigning one hash code to each server

One caveat with using load balancers for web applications is that if your servers are

stateful, you might run into a problem if you forgot about sticky sessions. But of course,

you’re building a RESTful API, which by definition is stateless, so this shouldn’t be a

problem, should it?

Just in case, let’s review.

When dealing with user sessions, the web server creates an in-memory object that

resides on the actual server that is serving your requests. This is all fine and dandy until

you get multiple servers working in parallel and, in theory, interchangeably with one

another. The problem here is that when you have all those servers with an in-memory

version of your session, you can’t really synchronize that data between all of them, so

in the end as shown in Figure9-2, they will have a partial version of the overall session

information and, for most part, will render it useless to you.

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288

Enter sticky sessions: a way of letting your balancers know to keep one client

associated to the same server after the first connection, that way the server-side session

can be retrieved and updated on every request. This is a very well-known technique, and

every load balancer has a way of dealing with this particular challenge.

You could also solve this by extracting your session management into a separate,

common service, such as a database (see Figure9-3), so every server would be able to

access and update session data independently.

Figure 9-2. Diagram showing classic problem with a fragmented session

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289

The only caveat with this approach is the extra work required to get the servers

working with the database (specially compared to using out-of-the-box features when

dealing with in-memory sessions).

Zone Availablity

Another way of achieving high availability in your application, especially if you’re

deploying into a Cloud service, is the ability to have your deployment either spread or

duplicated across multiple regions.

A very unpredictable and hard-to-overcome problem when you’re dealing with hosting

your applications with a third-party provider is that you don’t have any control over their

infrastructure, and if it fails, for any reason, you’re affected, whether you like it or not.

None of the major cloud providers will agree to a 100% uptime SLA (Service Level

Agreement, or put simply, and agreement between provider and consumer regarding

quality of the service), so no matter who you’re paying your hosting bills to, they will

eventually fail to provide. And that is when multi-zone deployments come in handy,

because usually downtimes on the cloud affect an entire geographical zone, so the

only way to get around this problem is by having your deployments replicated or

spread across several zones, effectively reducing the chances one of these geographical

problems will affect you.

Figure 9-3. Session information extracted into a common database

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290

This is a very common practice with managed database services. They usually also

allow you to pick which regions to replicate the data to, so in case of an outage, you’ll still

get your data, even if it’s a little bit slower. Look at Figure9-4 for a simple example of the

main differences between these two types of architectures.

Figure 9-4. Simple diagram showing the main differences between a replicated

and a spread architecture

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291

Both options take advantage of multi-zone setups, and they effectively got you

covered if something were to happen to some of the used zones. That being said, there

are some core differences, and deciding which one is the best match for your project is

completely up to you.

Let’s quickly look at some pros and cons of each case in Table9-2.

Doing theActual Deployment

After going over the basics, we’re now ready to look at some of the tools available to

us if we’re the ones in charge of deploying our code into production (or any other

environment, for that matter).

In this section I’ll go over two tools that will help you while uploading your code into

the server and then, once it’s already up and deployed, help you manage your processes

in production.

Table 9-2. Pros and Cons of Both Deployment Models

Deployment model Pros Cons

Replicated • Easier deployment, everything

deploys as one single block

• You only need one LB to pick the

right zone based on availability (at

least, you could also have other

criteria, such as latency).

• Simpler client–platform

communication

• Less exibility when it comes

to deployments and balancing

strategies

• If you’re dealing with in-memory

sessions, you need to congure

sticky sessions or use the

common database.

Spread • Extra exibility when it comes to

zone-dependent deployments

• Stronger fault tolerance. If API #1

fails, you don’t lose the current

transaction on API #2.

• A more complex deployment plan

than the replicated model

• Complex client–platform

communication, since you’d most

likely end up needing a load

balancer congured for each pair

of APIs.

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292

Shipit

Uploading your code to the server, whether it’s on the cloud or something on-premise,

can be as easy as an scp (a secure copy command that uses SSH authentication) or as

complicated as following a 20-step playbook. Hoping for the first with microservice-

based platforms is the the very definition of wishful thinking.

Fear not though, because there are many tools out there to help you automate

complicated deployments; they might not be easy the first time around, but subsequent

deployments should be considerably painless.

Shipit is exactly one of those tools, only one that is completely based on Node, so

you don’t need to install extra support for other languages in your system, something

you would have to do if you were to use other common tools, such as Capistrano

1

(which

requires Ruby to run).

With these tools, you can create simple tasks written in JavaScript that can then

be orchestrated from the command line. To be more specific, Shipit is actually a

combination of two tools: shipit-cli and shipit-deploy (which obviously you’ll

have to install before doing any of the following steps shown next). The first one is the

barebone core set of features, allowing you to create custom automation tasks (very

similar to other tools such as Gulp and Grunt), but the latter builds on top of the first

one and provides deployment-specific tasks, where you only need to configure a few

properties and then you’re done.

Let’s look at an example of a deployment task for shipit-deploy in Listing 9-1.

Listing 9-1. Example Deployment Task Using Shipit-Deploy

module.exports = function (shipit) {

require('shipit-deploy')(shipit);

shipit.initConfig({

default: {

workspace: '/tmp/your-project-name',

deployTo: '/path/to/deployment',

repositoryUrl: 'https://github.com/user/repo.git',

ignores: ['.git', 'node_modules'],

keepReleases: 3,

1

http://capistranorb.com/

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deleteOnRollback: false,

key: '/path/to/key',

shallowClone: true

},

staging: {

servers: 'user@staging-server.com'

},

production: {

servers: 'user@production-server.com'

}

});

};

To run the code from Listing 9-1, you save it into a file called shipitfile.js inside

your project and simply use the following command line:

$ npx shipit staging deploy --- to deploy to the staging server

Note The previous command is using the npx

2

cli tool, which is not directly

related to shipit. This tool allows you to run binaries from different modules,

checking if they’re locally or globally installed.

Let’s quickly go over the properties configured in the task on Table9-3.

2

See https://www.npmjs.com/package/npx

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294

For the complete list of options, please take a look at their documentation.

3

It is important to note that Shipit will create a particular folder structure on the target

server to properly manage the latest deployed version and as many as you specified in

the config file (remember the keepReleases property?). You can see the folder structure

in Listing 9-2.

Listing 9-2. Folder structure created by Shipit

/your/app/folder

|- current -> releases/20180429140211

|- releases

|-- 20180429140211

|-- 20180427130000

|-- 20171231200203

Table 9-3. List of Properties on Deployment Task

Property Description

default.workspace This is where shipit will download the code and do all the processing

before deploying it to the nal folder

default.deployTo This is the destination folder on your target server.

default.repositoryUrl This is where the code is coming from.

default.ignores Which les to ignore during the deployment

default.keepReleases How many releases should be kept back, in case a rollback is required

default.deleteOnRollback Your deployment went wrong, and you need to rollback. Do you delete

those no-longer-needed les? Hint: The answer is in this property.

default.key Path to your ssh pub key. This might be optional if you have your system

already congured with the default key in the right place.

default.shallowClone This is related to the depth of the git clone performed. Usually it’s a

good idea to leave it on TRUE.

staging.servers List of staging servers to which you want to deploy (That’s right, I said

servers, as in plural.)

production.servers Same as previous option, but for production servers

3

https://github.com/shipitjs/shipit-deploy/blob/master/README.md#options

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The root folder is the one specified in the deployTo property from Table9-3, but

shipit is not just dumping the code there; instead, it’s creating a new folder inside the

releases one, named using the current year, month, day, hour, minutes, and seconds of

the current timestamp.

The current directory is actually a symlink pointing to the latest folder created inside

releases. So at first, rolling back a version is as simple as re-pointing a linux symlink.

Cool, huh?

This approach is super flexible and powerful at the same time. It also simplifies other

tasks, such as configuring document roots in the web server, if you were to be deploying

a web app, since you’d also be setting it up to be /your/app/folder/current/public

(for instance), and no matter what the current active version is, you’ll always send back a

response with the web server on.

Installation

Finally, to install both utilities, you can do so, like this:

$npm install -g shipit-cli

$npm install -g shipit-deploy

What about Continuous Integration?

You might be wondering, what about CI? Isn’t that what this is supposed to be doing?

Why do I have to manually deploy?

And you’d be right, you can definitely set up a CI server that will take care of doing

this for you, but inside those automated tasks, you might end up configuring the

execution of Shipit tasks.

Just so we’re all on the same page, a CI server is one that can be configured to

automate your deployments (usually they’re language-agnostic, though they might have

language-specific plug-ins). People usually hook them up to code repository triggers,

so you can deploy by simply pushing into a specific branch. Some of the most common

CI servers are TravisCI,

4

Jenkins,

5

and Bamboo.

6

Figure9-5 shows an example diagram

of how that interaction would look.

4

https://travis-ci.org/

5

https://jenkins.io/

6

https://www.atlassian.com/software/bamboo

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With this set-up, you configure a post-commit hook on your git repository to

notify your CI environment when new code gets committed (this can also be done by

configuring your CI servers to check the repo periodically, looking for changes). Once

the CI tasks get triggered, your project will build, and this can mean anything, literally; it

all depends on you and the steps you want to take here.

Usually during this step, you’ll perform some testing tasks, such as running unit tests

to make sure the code you’re about to deploy actually works. This is such a common task

that CI platforms usually have plugins that will detect whether the tests failed or not, to

know if they can actually deploy the code or halt the deployment until you provide a fix.

The final step here would be to copy the code into the right place, and here is where

shipit comes again; you could simply have it pre-installed in your CI servers (depends

on the kind of access you have to them) and run your cli command using a task. If you

can’t install custom packages in your CI, which sometimes you can’t, you can probably

have it on your destination servers, and run the command remotely from your CI script.

Either way, Shipit is a tool that can be used independently or as part of your continuous

integration process.

PM2

Let me paint you a picture: You got your code ready, you managed to deploy it, and

much to your own surprise, it’s working! And minutes later, your platform is being

used. You sit down, sip on your very well-deserved cup of joe (the one that reads “Best

Figure 9-5. Sample interaction between your CI, a GIT repo, and your production

servers

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297

programmer in the w0r1d”—you earned it after all), and start thinking about the next

big project, pondering the new challenges that lie ahead, never wanting or needing

to look back at your old projects, hoping they’ll live happily and joyfully without your

intervention. Sounds nice, doesn’t it? Yeah… It’s all a lie though; you’ll never get that

happy ending, not unless you quit your job right after the first deployment.

Don’t go getting depressed on me now; it’s never going to happen, but that’s

normal. Nobody gets that happy ending, that is why tools such as PM2 exist. You need to

monitor and maintain your processes once deployed. Well, either you or someone from

another team needs to, but you get my point (usually developers don’t actively monitor

production systems, but they might be the ones fixing the issues in the end).

Why Do YouNeed aProcess Manager?

You technically don’t. Node.js is completely capable of functioning without one; that’s

not the point. The point here is that you’re on a production environment, and as we’ve

been covering during this entire chapter, failure here should not be an option, and if

(and when) it happens, you need all the tools at your disposal to (a) understand why it

happened, and (b) recover from it.

You can very well start your production process simply doing the good old:

$ sudo nohup node index.js & ---you'd be using sudo here to allow us to

listen on port 80

That will work, it’ll log your std.out into a nohup.out file, and thanks to nohup it

won’t close once you close the ssh connection to your server. But how much memory

are your processes consuming? What happens if they crash due to a bug, or a lack of

resources, or something else? Really, you got your process up and running, but that’s as

far as you’ll get. This is far from ideal and a place where you generally don’t want to be.

So, What Now?

Enter PM2, a process manager capable of keeping your processes alive and monitoring

them at the same time. It provides a rich command line tool, web interface, and even the

ability to use Node’s cluster API on your processes without having to change their code.

To install it, you can simply:

$ npm install pm2 -g

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After that, you can start monitoring your application by starting it with PM2 (as seen in

Figure9-6), like so (Listing 9-3 shows an actual program that we’ll monitor using pm2):

$pm2 start index.js --name "my app" -i max

The output shown on Figure9-6, is what you would see if you started your

application on a similar system as mine. Decomposing the start command, you can see

that the --name parameter is used to provide a human readable identifier that can be

used to reference the entire group of processes. The -i max modifier tells PM2 to use the

maximum amount of cores in your system (mine has four), so right off the bat, we’re

clustering the application, without having to even think about it on our code (look at

Listing 9-3 as proof).

Tip You can start your application with a pre-defined memory limit (using the

--memory-max-restart [limit][M|G|K] modifier). If you do, PM2 will

restart your process once it reaches that limit.

Note All processes are now being actively monitored by PM2, and if any of them

crashes for any reason, it’ll be automatically restarted.

Listing 9-3. Sample Program Used on the PM2 Start Example

const http = require('http');

function serve(ip, port)

{

http.createServer( (req, res) => {

console.log("[LOG] Request received");

Figure 9-6. Output from the pm2 start command

CHAPTER 9 DEPLOYING INTO PRODUCTION

299

res.writeHead(200, {'Content-Type': 'text/plain'}); // Return a 200

response

res.write(JSON.stringify(req.headers)); // Respond with

request

headers

res.end("\nServer Address: "+ip+":"+port+"\n"); // Let us

know the

server that

responded

}).listen(port, ip);

console.log('Server running at http://'+ip+':'+port+'/');

}

serve('0.0.0.0', 9000);

Logging with console.log is not a great idea usually, because you can’t really do

much with the console output, but if you’ve decided to stick to that, PM2 captures

anything thrown at stdin and stoud, so with a simple:

$ pm2 logs

you’ll get the last 15 lines of logs for each process (as seen in Figure 9-7). You can also

specify the id of the process for which you want to see the logs.

Figure 9-7. Output from pm2 logs

You also have your basic commands such as pm2 restart "my app" if you want to

restart all your API processes. Or pm2 stop "my app" if you need the manager to stop all

processes.

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300

Another helpful command is the pm2 monit one, which brings up a console UI with

general monitoring features. As you can see on Figure9-8, you get a global overview of

the system, with the possibility of browsing through that data using your arrow keys.

The last feature I’d like to cover in this chapter (you should definitely look into the

main documentation,

7

since there is quite a lot I’m leaving out) is the process metrics.

With this feature, you can register a function in your code to provide a metric that can be

read from PM2 monitoring UI.

Let’s take a look and add a request counter to the previous code—something simple

to get us started. To get this to work, you first need to install the pmx module; after that

you can update the code as follows:

Figure 9-8. Console UI for monitoring the current status of your processes

7

http://pm2.keymetrics.io/docs/usage/quick-start/

CHAPTER 9 DEPLOYING INTO PRODUCTION

301

Listing 9-4. Custom Metric Code Added to the Example

const http = require('http');

const Probe = require("pmx").probe();

let REQUEST_COUNTER = 0;

Probe.metric({

value: () => REQUEST_COUNTER

});

function serve(ip, port)

{

http.createServer( (req, res) => {

console.log("[LOG] Request received");

REQUEST_COUNTER++;

res.writeHead(200, {'Content-Type': 'text/plain'}); // Return a 200

response

res.write(JSON.stringify(req.headers)); // Respond with

request

headers

res.end("\nServer Address: "+ip+":"+port+"\n"); // Let us

know the

server that

responded

}).listen(port, ip);

console.log('Server running at http://'+ip+':'+port+'/');

}

serve('0.0.0.0', 9000);

You can get the metric’s value using pm2 show [ID] to get a snapshot of the entire

process, or start the monitoring UI and get a real-time view of the metrics.

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Summary

In this chapter, we covered the basic concepts to take into account when creating your

production environment and when (and how) to promote code from one environment

to the other.

In the next and final chapter, I’m going to cover some basic troubleshooting for this

type of application.

Figure 9-9. Monitoring UI showing custom metrics values

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F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1_10

CHAPTER 10

Troubleshooting

This is it. You made it to the final chapter. You experienced first-hand what it takes

to write a RESTful API in Node. You’ve gone over the theory. You learned what REST

actually stands for and how to use it to develop a good and useful API.

In this chapter, I’ll cover some of the things that can go wrong during the process and

some of the considerations you have to take into account, such as the following:

• Asynchronous programming: I’ll take one final shot at this subject,

explaining how it was used in our code.

• Minor details about the Swagger UI conguration: Sometimes the

documentation is not enough.

• Potential CORS issues: I’ll go over the basics of CORS to help you

understand how to use it to your advantage.

• Data types: e last subject that I’ll cover regarding our code is how

to go from JSON Schemas data types to Mongoose types.

Asynchronous Programming

For the mind of the non-JavaScript developer, or even for the non-Node.js developer,

the concept of asynchronous programming might be a strange one to grasp at first. And

I say “might” because it’s not a JavaScript/Node.js–unique concept; other programming

languages, like Earlang, Python, and even the more recent Go have this capacity.

That being said, Node.js is one of the few environments where a web developer is

kind of forced to deal with this concept or is unable to properly develop.

Asynchronous programming becomes a must on any mid-sized project using Node.

js when you start dealing with external resources, mainly because that means you’ll

be using third-party libraries that are already taking advantage of this programming

technique; so you either embrace it or switch languages.

304

You’ve already covered how this feature improves the performance of applications,

and you even saw a couple of useful design patterns that leverage it, so let’s now discuss

how failing to grasp this concept could hurt your understanding of the code presented in

Chapter 7.

Whether or not you’ve noticed, in our API’s code, there are several places where

asynchronous programming takes place. Let’s look at some of them.

The Controllers Action’s Code

Every action on every controller has a piece of asynchronous programming in the form

of database queries. This is probably the most obvious bit, but it’s important to go over it

to understand it properly.

The reason why we don’t do anything like Listing 10-1.

Listing 10-1. Example of a Database Query Inside One of Our Controllers

(authors.js file)

var authors = lib.db.model('Author')

.find(criteria).exec()

if(!authors) return next(controller.RESTError('InternalServerError',

authors))

controller.writeHAL(res, authors)

And instead, we set up a call-back function, like shown in Listing 10-1:

lib.db.model('Author')

.find(criteria)

.exec((err, authors) => {

if(err) return next(controller.RESTError

('InternalServerError', err))

controller.writeHAL(res, authors)

})

This is because, as I’ve already stated, I/O operations in Node.js are asynchronous,

which means that querying the database needs to be done like this, with a call-back

function set up to handle the response once it arrives. It is true that Node.js provides

synchronous versions of its I/O functions (like reading and writing files), but they’re

CHAPTER 10 TROUBLESHOOTING

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mostly there to simplify the transition; you’re not being encouraged to use them, and

third-party libraries like Mongoose aren’t interested in following that pattern either.

Catching this type of error while manually testing your application might be a bit of a

headache, because the resulting behavior might not always be the same. When the code

is complex enough, it becomes a race between the time it takes for the asynchronous

function to get a response back and the time it takes for your code to use that value.

Also, because the Node.js interpreter won’t throw an error if you miss some of the

parameters on a method/function call, you might end up doing something like that in

Listing 10-2.

Listing 10-2. Sample Code Showing Missing Attributes

const fs = require("fs");

function libraryMethod(attr1, callback) {

fs.readFile(attr1, function(err, response){

if(callback) callback(response)

})

}

var returnValue = libraryMethod('index.js')

The code from Listing 10-2 will not throw an error—ever. And you’ll always get

undefined in your returnValue. And if you don’t have access to the code of the

libraryMethod function, it might be difficult to understand what’s wrong.

For instance, you have a code like in Listing 10-3.

Listing 10-3. Example of an Incorrect Asynchronous Code that Works Correctly

Sometimes

const fs = require("fs");

const request = require("request");

let myResponseValue = ''

fs.readFile('./yourfile.txt', (err, response) => {

myResponseValue = response

})

CHAPTER 10 TROUBLESHOOTING

306

//The time for the following request might vary, and the results with it

request.get('http://www.google.com', () => {

console.log(myResponseValue)

})

Listing 10-3 shows another common mistake when working with asynchronous

calls: you properly set up the call-back, but you used the returned value outside of that

callback.

In the preceding example, if the readFile call takes less than the request to Google

to get a response, it’ll work, but you won’t realize your mistake until something happens

(such as the code going to production). Suddenly, readFile is reading a larger file than

expected, thus taking longer to finish, and now an empty string is always printing to the

console. But you don’t know why, of course. The simple way to fix this is to add any code

dealing with the response value inside the callback function.

The Middleware Functions

This might not be obvious at first glance, but the entire middleware chain is following the

serial flow mechanics mentioned back in Chapter 3. How can you tell? Because of the

next function; you need to call it when the function is over and ready to give control to

the next middleware.

You can have even more asynchronous code inside the function and still be able to

call the next function, thanks to next.

In some places this isn’t really visible, like when setting up the queryParser and

bodyParser middleware:

server.use(restify.plugins.queryParser())

server.use(restify.plugins.bodyParser())

But those methods are actually returning a new function, which in turn receives the

three magic parameters: the request object, the response object, and the next function.

A common issue when creating custom middleware is forgetting to call the next

function (see Listing 10-4 for an example) in one of the possible execution branches of your

code (if you happen to have them). Symptoms of this are that your API appears to hang up,

you never get a response back from the server, and you don’t see any errors on the console.

This is due to the fact that the execution flow is broken. Suddenly it’s unable to find a way to

continue, and you’re not sending back a response (using the response object).

CHAPTER 10 TROUBLESHOOTING

307

This is tricky to catch, since there aren’t any error messages to clearly state the

problem.

Listing 10-4. Example of an Ill-constructed Middleware Function

function middleware(req, res, next){

if(req.params.q == '1') {

next()

} else {

if(req.params.q2 == '1') {

next()

}

Looking at Listing 10-4 we can infer that if no “q” or “q2” parameters are sent, or if

they don't have the right values, then this middleware function is breaking the serial flow

and no response is ever getting back to the client.

There is another type of middleware used on the project: Mongoose middleware,

which are the hooks you can attach to models to be executed before or after a set of

specific actions. Our particular case used a post-save hook on the clientreview model,

see Listing 10-5 for an example.

Listing 10-5. Sample Middleware Function Used with MongooseJS

modelDef.schema.post('save', function(doc, next) {

db.model('Book').update({_id: doc.book}, {$addToSet: {reviews:

this.id}}, next

)

})

This code clearly shows the next function being used in conjunction with an

asynchronous call inside the middleware. If you were to forget to call next, then the

execution would be interrupted (and halted) at this call-back.

CHAPTER 10 TROUBLESHOOTING

308

Issues Configuring theSwagger UI

Setting up the Swagger UI is a task that requires both a change to the UI itself and some

special code on the back end. This is not particularly easy to understand since the

documentation is not exactly simple to read.

On the one hand, we’re using the swagger-node-restify module to generate the back-

end endpoints needed by the UI; this is achieved in the following lines in the index.js file

from Chapter 7:

1. swagger.addModels(lib.schemas)

2. swagger.setAppHandler(server)

3. lib.helpers.setupRoutes(server, swagger, lib)

4. swagger.conﬁgureSwaggerPaths("", "/api-docs", "")

5. swagger.configure('http://localhost:9000', '0.1')

Line 1 sets up the models, so that Swagger can return them when the endpoints

specify them as the response class. Line 2 is basically telling the module which web

server we are using for the documentation. We could potentially have two different

servers configured: one for the documentation and one for the actual API.

Line 3 is actually one of ours, but it does require Swagger, because we’re calling

the addGET, addPOST, addDELETE, or addPUT methods provided by it. This is done by the

BaseController code in its setUpActions method, with the code from Listing 10-6.

Listing 10-6. Snippet from Chapter 7 Showing Where We Deal with Swagger’s

Methods

this.actions.forEach(act => {

let method = act['spec']['method']

logger.info(`Setting up auto-doc for (${method} ) - ${act['spec']

['nickname']}`)

sw['add' + method](act)

app[method.toLowerCase()](act['spec']['path'], act['action'])

}).

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309

Line 4 doesn’t really say much, but it’s useful for several reasons:

• The most obvious one is that we’re setting up the path for the

documentation: /api-docs.

• We’re also saying that we don’t want to specify formats via extension

(i.e., .json). By default, we need to define a {format} section in

our path to be autoreplaced by .json. With this specific line, we’re

removing the need for that and simplifying the path formats.

Finally, line 5 sets the base URL for the entire documentation API.

In Chapter 7, the front-end code had to change; I mentioned where exactly.

Uncommenting the code for the API key and the change in the host URL are obviously

needed, but the change in the resource path isn’t. We need to change this because of the

way we configured the static path during the initialization phase (check Listing 10-7 for

more details).

Listing 10-7. Code Used to Set Up the Static Route to Return Swagger’s UI

server.get(/^\/swagger-ui(\/.*)?/, restifyPlugins.serveStatic({

directory: __dirname + '/',

default: 'index.html'

}))

Note The code from Listing 10-7 uses the special variable __dirname, which

even though we’ve not defined, is already available and contains the current

working directory of the executed script.

The code from Listing 10-7 ensures that only anything under the swagger-ui folder

is served as static content (which is basically everything that the Swagger UI needs), but

the default path that comes in the HTML file points to the root folder, which isn’t good

enough in our case.

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310

CORS: a.k.a. Cross-Origin Resource Sharing

Any web developer who’s been at it for a while has seen this dreaded error message:

XMLHttpRequest cannot load http://domain.example. Origin http://domain1.

example is not allowed by Access-Control-Allow-Origin.

For developers working on a web client for a public API, the browser checks for cross-

origin resource sharing (CORS) to make sure that the request is secure, which means

that the browser checked the requested endpoint and since it’s not finding any CORS

headers, or the headers don’t specify our domain as valid, it is cancelling the request for

security reasons.

For API designers, this is a very relevant error because CORS needs to be taken into

account, either by manually allowing it or by denying it.

If you’re designing a public API, you need to make sure that you specify in the

response headers that any domain can make a request. This is the most permissive of all

possible settings.

If, on the other hand, you’re defining a private API, then the CORS headers help

define the only domains that can actually request any kind of resource of the endpoints.

Normally, a web client will follow a set of steps on every CORS request:

1. First, the client will ask the API server if the desired request is

possible (Can the client query the wanted resource using the

needed method from the current origin?). This is done by sending

a “pre-flight”

1

request with the Access-Control-Request-Header

header (with the headers the client needs to access) and the

Access-Control-Request-Method header (with the method

needed).

2. en the server will answer with what is authorized, using these

headers: Access-Control-Allow-Origin with the allowed origin

(or * for anything), Access-Control-Allowed-Methods with the

valid methods, and Access-Control-Allow-Headers with a list of

valid headers to be sent.

3. Finally, the client can do the “normal” request.

1

An OPTIONS request.

CHAPTER 10 TROUBLESHOOTING

311

If anything fails to validate during the pre-flight request (either the requested

method or the headers needed), then the response will not be a 200 OK response.

For our case, according to the code in Chapter 7, we’re going for the public API

approach, since we’re allowing any domains to do requests to our endpoints with the

code in the index.js file shown in Listing 10-8:

Listing 10-8. Example Code Used to Set the CORS Headers on Every Endpoint of

Our API Data Types

restify.defaultResponseHeaders = data => {

this.header('Access-Control-Allow-Origin', '*')

}

Even though we’re not directly handling and specifying types for our variables

throughout the API’s JavaScript code, there are two very specific places where data types are

needed: the JSON Schemas defined for our resources and the Mongoose models defined.

Now, thanks to the code in the getModelFromSchema function and the

translateTypeToJs function, you can go from JSON Schema types to Mongoose types

because most of the basic types defined in our schemas are almost directly translatable

into JavaScript types.

For the more complex types, like arrays, since the entire definition is different, extra

code needs to be added, which is where the getModelFromSchema code comes in.

The type’s translation from the code in Chapter 7 is limited to what was needed at

the time, but you could easily extend it to achieve further functionalities, like getting the

required attribute to work for both the schema validator and the Mongoose validators

(these make sure you don’t save anything invalid). Let’s quickly look at how to go about

adding support for the required property.

An object type is composed of a series of properties but also a list of required

properties, which is defined at the same level as the properties attribute. Take a look at

Listing 10-9 for an example of that:

Listing 10-9. Example Showing how to Set Two Attributes (Name and Website)

as “Required” in the JSON Schema

module.exports = {

"id": "Author",

"properties": {

"name": {

CHAPTER 10 TROUBLESHOOTING

312

"type": "string",

"description": "The full name of the author"

},

"description": {

"type": "string",

"description": "A small bio of the author"

},

"books": {

"type": "array",

"description": "The list of books published on at least one of

the stores by this author",

"items": {

"$ref": "Book"

}

},

"website": {

"type": "string",

"description": "The Website url of the author"

},

"avatar": {

"type": "string",

"description": "The url for the avatar of this author"

},

"address": {

"type": "object",

"properties": {

"street": {

"type": "string"

},

"house_number": {

"type": "integer"

}

CHAPTER 10 TROUBLESHOOTING

313

}

},

"required": ["name", "website"]

}

To get the content of this new property, you just need to add a few lines to the

getModelFromSchema function to simply check for the property name; and if it’s inside

the required array, you set it as required. See Listing 10-10 for more details.

Listing 10-10. Single Line Added to the Function (Inside lib/db.js File) to Allow

Support for Required Attributes

function getModelFromSchema(schema) {

let data = {

schema: {}

}

let newSchema = {}

let tmp = null

_.each(schema.properties, (v, propName) => {

v.required = schema.required && schema.required.indexOf(propName)

!= -1;

if(v['$ref'] != null) {

tmp = {

type: Schema.Types.ObjectId,

ref: v['$ref']

}

} else {

tmp = translateComplexType(v)

}

newSchema[propName] = tmp

})

data.schema = new Schema(newSchema)

return data

}

CHAPTER 10 TROUBLESHOOTING

314

Summary

This is it. You made it. And you managed to go through the entire book! You went from

the basics of REST to a full-blown RESTful API.Finally, in this chapter, you learned

the main things that can cause trouble during the development process, such as

asynchronous programming, configuring the Swagger UI, CORS, and moving from JSON

Schema types to Mongoose types.

Thank you for reading and, hopefully, enjoying the book.

CHAPTER 10 TROUBLESHOOTING

315

F. Doglio, REST API Development with Node.js, https://doi.org/10.1007/978-1-4842-3715-1

Index

A

addAction method, 200, 244

API design

description, 39

Developer eXperience (DX)

access points, 41–42

communication protocol, 40–41

uniform interface, 42–45

error handling

client development stage, 53–55

end users, 55–56

extensibility

Chromium project, 48

Facebook APIs, 46

Google APIs, 46

Semantic Versioning, 49

Twitter APIs, 46

versioning scheme, 49

versions of API, 46–48

scalability

bookstore, 69

distributed architecture, 68–69

entities, 69

estimation, 66

monolithic architecture, 66–67

SDK/libraries, 56–57

security

authentication, 57

authorization, 57

Basic Auth, TSL, 58–59

Digest Auth, 60–61

MAC signing process, 65

OAuth 1.0a, 62–63

OAuth 2.0, 64

RESTful systems, 57

stateless methods, 58, 64–65

up-to-date documentation

4chan’s API

documentation, 51–52

Facebook’s developer site, 51

Mashape service, 50

optional parameters, 50

success/failure reasons, 52

api_key parameter, 193

Asynchronous programming

benets, 74

callback function, 72

controllers action’s code, 304–306

error reports, 75

execution ow, 74

instructions, 73

I/O operation, 81–84

middleware functions, 306–307

Node.js, 303

parallel function, 76–79

serial ow, 79–80

simple le read operation, 75–76

B

body parser, 258

316

C

Cacheable constraint, 6–7

Classical development cycle, 283–286

Client–Server architecture, 4

Code-on-demand, 10

Continuous Integration (CI), 295–296

controllers folder

Authors, 214–219

BaseController, 198–200

Books, 200–207

BookSales, 219–221

ClientReviews, 221–222

Clients, 222–225

Employees, 225–228

index, 197

Stores, 207–214

Cross-origin resource

sharing (CORS), 310–313

D

Database storage system

easy-to-change schemas, 185–186

handle entity relations, 185–186

integration, 185–186

preparation process, 188

Sequelize and Mongoose, 187

speed of development, 185

Data transfer object (DTO), 187

Deployment

CI server, 295–296

PM2

console UI, monitoring, 300

custom metric code, 301

install, 297

logs, 299

monitoring, 298

monitoring UI, custom metrics, 302

output, start command, 298

process manager, 297

sample program, 298

Shipit (see Shipit)

Developer eXperience (DX)

access points, 41–42

communication protocol, 40–41

uniform interface

access points, 42

endpoints, 42–43

inconsistent interface, 42

JSON, 44–45

Duck typing, 94

Dynamic typing, 88

E

Express.js modules

callback function, 135–136

content of app.js, 133

generator commands, 132

global middleware, 137

handler function, 134

information, 131

regular expressions, 135

route-specic middleware, 137

F

Folder structure

cong, 196

controllers, 195

lib, 195

models, 195

node_modules, 196

request_schemas, 196

Index

317

schemas, 196

set up, 194

swagger-ui, 196

G

getModelFromSchema

function, 235, 237

getStoresBookSales, 214

H

HAL modules, 163–167

Halson modules, 160–163

HAPI modules, 126–130

Hierarchical MVC, 112–114

hmacdata header, 193

HTTP status codes, 26–27

Hypermedia as the Engine of Application

State (HATEOAS), 20

Hypertext Application

Language (HAL), 23–25

I

I/O Docs modules

API conguration, 156

custom documentation,

web UI, 160

documentation server, 155, 159

docummented APIs, 157

information, 155

JSON le, 158–159

J, K

JSON-Gate module, 167–169

jsonSelect model, 238

L

Layered system constraint, 9

lib folder

cong, 237

db, 232–235

helpers, 229–230

logger, 236

schemaValidator, 231–232

M

MAC signing process, 65

makeHAL function, 231

Mocha

asynchronous test case, 277–278

BookSales controller, 278–282

installing, 276–277

testing libraries, 275

models folder

author, 237–238

books, 239–240

booksale, 240–241

client, 241

clientreview, 241–242

employee, 242

index, 237

store, 242–243

Model–view–adapter (MVA) pattern, 116

Model–view–controller (MVC) pattern, 194

architecture, 107, 110–111

decoupling components, 109

HMVC, 112–114

layers, 107–109

MVA pattern, 116

MVVM pattern, 115

overview, 107

web development frameworks, 110

Index

318

Model–View–ViewModel (MVVM )

pattern, 115

Modules

attributes, 125

Express.js

callback function, 135–136

content of app.js, 133

generator commands, 132

global middleware, 137

handler function, 134

information, 131

regular expressions, 135

route-specic middleware, 137

HAL, 163–167

Halson, 160–163

HAPI, 126–130

hypermedia response, 125

I/O Docs

API conguration, 156

custom documentation,

web UI, 160

documentation server, 155, 159

docummented APIs, 157

information, 155

JSON le, 158–159

JSON-Gate, 167–169

middleware functions, 123–124

request/response handling, 122

response/request validation, 125

Restify

content negotiation, 142

information, 138

naming routes, 139–141

options, 139

versioning routes, 141

Web Server Creation, 138

routes handling, 122–123

swagger-node-express, 148–154

TV4, 169–172

up-to-date documentation, 125

Vatican.js

command line actions, 145

constructor options, 145

endpoint, REST methods, 146–147

index.js, 144

information, 143

list command, 148

middleware function, 148

MongoDB integration, 144

resource generator command, 145

Mongoose Schema, 235, 238, 245

Monolithic design, 66–67

MySQL, 185, 186

N

Node.js

asynchronous programming

benets, 74

callback function, 72

error reports, 75

execution ow, 74

instructions, 73

I/O operation, 81–84

parallel function, 76–79

serial ow, 79–80

simple le read operation, 75–76

classes in ES6, 91–92

duck typing, 94

dynamic typing, 88

functional programming, 93–94

JavaScript, 87–88

JSON, 95

npm, 96–97

prototypal inheritance, 199

object orientation, 89–90

Index

319

RESTful systems, 98

scripting languages, 87

speed of development, 71

synchronous programming

execution ow, 72–73

I/O operation, 85–87

users, production, 98

web server, 88

Node Package Manager (npm), 96–97

O

Object-relational mapping (ORM), 186

P

Planning

bookstore chain, 174–176

database storage system

easy-to-change schemas, 185–186

handle entity relations, 185–186

integration, 185–186

Sequelize and Mongoose, 187

speed of development, 185

endpoints, parameters and HTTP

methods, 180–182

features, 177

preparation process, 188

problems, 173–176

resources, properties, and

descriptions, 178–179

UML diagram, 183–184

PostgreSQL, 185, 186

Post-processing chain, 118, 119

Production

classical development cycle, 283–286

environments, 283–284

high availablity, 286

load balancers

distributing incoming trac, 287

fragmented session, 287–288

horizontal scaling, 287

server-side session, 288

session information, common

database, 288–289

user sessions, 287

vertical scaling, 287

web applications, 287

zone availablity

Cloud service, 289

pros and cons, deployment

models, 291

replicated and spread

architecture, 290

SLA, 289

third-party provider, 289

properties attribute, 311

Prototypal inheritance, 199

Q

query parser, 258

R

REpresentational State Transfer (REST)

architecture, 101

MVC pattern (see Model–view–

controller (MVC) pattern)

pre-processing chain, 103–106

request handler, 102–103

response handler, 116–119

benets, 3

cacheable constraint, 6–7

client-server constraint, 4

code-on-demand, 10

Index

320

complex actions

collections, 17–18

complexity, 17

CRUD actions, 16

multi-entity searches, 19

single-entity searches, 19

URIs, 16

URLs, 16

content negotiation, 13

CRUD actions, 15

denition, 2

le extensions, 13

HAL, 23–25

HTTP protocol, 2

HTTP status codes, 26–27

HTTP verbs and proposed actions, 15

hypermedia and main endpoint

client application, 22

HATEOAS, 20

hyperlinks to resources, 21–22

JSON structure, 23

metadata, 20

resources, 23

root endpoint, 20–21

web browser, 20

interface, 3

layered system constraint, 9

Microsoft, 28

modiability components, 3

performance, 2

planning (see Planning)

portability, 3

protocol-independent, 1

reliability, 3

resources

control data, 11

denition, 11

identier, 11, 14

metadata, 11

representations, 11–12

structure description, 11

RFC, 2

scalability, 3

SOAP request, 30–31

stateless constraint, 5–6

system interoperability, 28

uniform interface constraint, 7–8

visibility, 3

W3C SOAP spec page, 32

WSDL, 32–35

XML-RPC

architecture, 29–30

request, 28–29

response, 29

SOAP, 36

Request for Comments (RFC), 2

request_schemas folder

booksales, 244

controller name, 244

endpoint nickname, 244

getBookSales endpoint, 243

JSON Schema, 243–244

type of object, 244

Response handler

nal architecture, 118–119

HTTP response, 116–117

post-processing chain, 118

REST API development

folder structure, 194–196

minor simplications

adding Swagger UI, 192

backdoor for Swagger, 193–194

REpresentational State

Transfer (REST) (cont.)

Index

321

employee relationship, 192

MVC, 194

plan changes, 192

security, 193

source code

cong, 196–197

controllers (see controllers folder)

lib (see lib folder)

models (see models folder)

request_schemas, 243–244

root folder (see Root folder)

schemas (see schemas folder)

swagger-ui, 254

stages, 191

RESTError method, 200

Restify modules

content negotiation, 142

information, 138

naming routes, 139–141

options, 139

versioning routes, 141

Web Server Creation, 138

Root folder

index.js, 256–258

initial section, 258

middleware setup, 258

package.json, 255

setup section, 258–259

S

Scalability, API design

bookstore, 69

distributed architecture, 68–69

entities, 69

estimation, 66

monolithic architecture, 66–67

schemas folder

Author, 248

Book, 249–250

BookSale, 250–251

Client, 251–252

ClientReview, 245–246

Employee, 252–253

index, 247

Mongoose Schema, 245

Store, 253–254

Security, API design

authentication, 57

authorization, 57

Basic Auth, TSL, 58–59

Digest Auth, 60–61

MAC signing process, 65

OAuth 1.0a, 62–63

OAuth 2.0, 64

RESTful systems, 57

stateless methods, 58, 64–65

security check, 259

Semantic Versioning (SemVer), 49

server start section, 258

Service Level

Agreement (SLA), 289

setUpActions method, 200

setupRoutes function, 207, 230

Shipit

Capistrano, 292

deployment task

properties, 293–294

shipit-deploy, 292–293

folder structure, 294–295

installation, 295

shipit-cli and shipit-deploy, 292

uploading code, 292

Index

322

SOAP request, 30–31

Standard Environments for Web-Bbased

Software Projects, 284

stars attribute, 246

Stateless constraint, 5–6

Stateless methods, 58

static content folder, 259

swagger-node-express

modules, 148–154

Swagger-UI

addition, 192–193

backdoor for, 193–194

troubleshooting, 308–309

swagger-ui folder, 254–255

Synchronous programming

execution ow, 72–73

I/O operation, 85–87

T

Testing API

assertions, 264–265

database interaction, 265–266

denition, 261–263

dummies, 270

external service, 266

xtures, 270

mocks, 268–269

Node.js

deepStrictEqual(actual,

expected[, message]), 273–274

Mocha (see Mocha)

modules, 272

ok(value[, message]), 273

throws(block[, error][,

message), 274–275

production systems, 265

recommendations, 271

software development, 266

spies, 269–270

stubs, 267–268

test cases and test suites, 264

toHAL method, 238

Transport language, 44

Troubleshooting

asynchronous programming

controllers action’s code, 304–306

middleware functions, 306–307

Node.js, 303–304

CORS, 310–313

JSON Schema types, 311

Mongoose types, 311

Swagger UI, 308–309

TV4 module, 169–172

U

Uniform interface constraint, 7–8

Unique resource identier (URI), 14

V

validate check, 259

validateKey function, 231

Vatican.js modules

command line actions, 145

constructor options, 145

endpoint, REST methods, 146–147

index.js, 144

information, 143

list command, 148

middleware function, 148

MongoDB integration, 144

resource generator command, 145

Index

323

W

Web Service

Description Language

(WSDL), 32–35

writeHAL

method, 200, 281

X, Y, Z

XML-RPC

architecture, 29–30

request, 28–29

response, 29

SOAP, 36

Index